Inability to access your data stored on the data storage device could be caused by many reasons, from those that are easy to fix to those which are completely impossible to fix. If the damage is irreversible then data loss will occur. The causes of the failure of your hard drive or CD-ROM drive could vary from a bad connection due to a loose wire (which is easily recoverable) to damage to the media itself, which could still be recoverable in many cases.

If the damage occurred to the drive's electronics, it most likely could be fixed. If the damage occurred to the, for example, system areas of the disk, leaving the data zone intact, those data could be theoretically, and (in some cases) practically, recovered by a professional. But, if the data zone is damaged, the data in the damaged area will not be recovered since the loss of data has already taken place. In this case, one can only rely on the back-up...

There are two major reasons for your data storage device failure: poor handling and manufacturing defects.

Poor handling:
Even if the today's hard drives, for example, are capable of handling operational shock up to 300 G, their electronics or mechanical components still could be damaged by the vibration or by an impact. Liquid spilled on the drive may short electric connections or even penetrate inside the drive, especially inside the drives with removable media (Zip, CD-everything, Tape drives, etc.).

Contamination of the drive's insides by dirty media or the environment could speed up mechanical wear or result in immediate failure. One possible reason for damage to the drive's electronics is an electro-static discharge, a so called ESD, which often happens between your fingers and the drive's body. During this discharge a large potential can be generated at the very small gaps and in small areas causing heat dissipation, melting and disintegration of the IC elements. This is why most electronics and storage devices are shipped inside a special ESD-protecting plastic bags. When handling the drives, try to keep your other hand on a metal part of your PC such as the frame, which will serve as a "ground". Also, touch the metal part of your PC with both hands before handling any ESD-sensitive device.
Manufacturing defects:
Unfortunately, even those of us who handle things with great care are not immune from disaster. All media, drives and storage system components undergo thorough testing, but in spite of this, statistics guarantees a few bad drives among hundreds of good ones... You may be unlucky and buy one of those. But even in this case, data back-up and a good manufacturer's warranty can make losses partially or completely recoverable.

How to prevent data loss?

The best prevention is to always remember to back-up your data!
Accidents may happen: coffee is spilled on your CD or Zip drive, a CD falls on the floor and gets scratched, the hard drive does not want to spin after being unused during 2 humid summer months, ... Anything may happen, but you should not worry if your most valuable data is stored separately in a safe place.
Another thing to remember is to use anti-virus software routinely, especially if you download from the Internet! Your data could be as easily corrupted by a computer virus as by any natural disaster. To protect your data from the newest viruses, update your antivirus program as often as possible.
Prevent impacts on your storage device, especially when it is running! For example, don't move your desktop when the power is on! All commercial storage systems are designed to withstand significant shock and vibration, but there is always a chance that your drive may be damaged by an impact.
Avoid electro-static discharge (ESD) during installation of the drives and later handling. Do not touch electric contacts on the controller board with your bare hands. When handling the drives, try to keep your other hand on a metal part of your PC, which will serve as a "ground".
Keep your storage systems clean!
Particulate contamination is a clear and present danger for all types of storage media since is causes mechanical damage which is rarely recoverable and can crash the entire storage device!
Keep your data cool!
Storage systems, especially magnetic media, may suffer from the so-called 'thermal decay' of magnetic information. In other words, your magnetic domains will lose their magnetization much faster at higher temperatures, and your bits of information will disappear... Magnetic drives are designed to operate in conditions comfortable for humans. Therefore, there is no danger in keeping your drives at 40 (104F) and even 50C (122F). But, exceeding this temperature by much can be harmful.
Keep away your magnetic storage from strong magnetic fields!

What to do if it has already happened?

The main rule is simple:
if the data you are about to lose are really important to you, do not experiment with the damaged media for too long! You may further damage it beyond recovering.

Floppy disks

Floppy diskettes are designed to be robust and to operate in an unfriendly environment filled with dirt, abrasive particles, moisture, etc. But, still, the environment and the way we handle floppy disks may result in damage.

new floppy Low magnification (X 25) image of the scratch on the floppy disk surface.

If you cannot read from a new floppy disk, it just may need formatting! But, make sure there is no data on the floppy disk - formatting will definitely erase all the data forever! Nowadays most floppy disks are sold pre-formatted for IBM-type PCs or for the Macintosh. Check if the operating system marked on the floppy box is same as operating system you are using.
If you can not write to the floppy, check if the switch on the back of the floppy is in write-protect mode. If it is, switch it to another position.
Next, try to read this floppy using another floppy drive (ask a friend or colleague), maybe the problem is in the drive, not in the floppy.
Next, slide the metal window on the floppy aside and check the surface for damage. Usually, the surface will appear as a dark mirror, and you can easily see if there is a circumferential scratch on the surface.
If there is a scratch, you have mechanical damage to your magnetic media. One can rarely recover data from mechanically damaged areas since the magnetic bits may not exist there anymore. But, there is still a chance to recover data on the other parts of the disk. If these data are valuable to you, do not try anything else on your own. Contact professional data recovery services.
If there is no visible scratch, there could be some particle or dirt stuck to the disk surface. It is sometimes helpful to blow air on the disk surface through the open metal window. You may simultaneously gently rotate the disk to treat the entire surface. Be careful, don't spit on the disk accidentally! After you are done, try reading from this floppy again. If it does not work, contact professionals in data recovery.
If your floppy drive won't work, start your CMOS Setup and check the BIOS setting for the floppy drive. If A: (or B:) drive is set as none or not installed, the drive will not work. Change the settings and save them before exiting, if necessary.
If this does not work, check the cables. Check the power cable for a bad connection, and check the twisted cable for the correct configuration: drive A: should be connected to the end-most connector (after the cable twist) and drive B: to the middle connector (before the twist).
If this does not help, replace the twisted cable.
Finally, to make sure that the problem is in the drive, check to see if a different floppy drive will work in the same place.

Zip disks, etc.

Zip and similar products are also designed to be robust and operate in an unfriendly environment filled with dirt, abrasive particles, moisture, etc. Plus, they work at a much higher rotational velocity (~3000 rpm vs. 300 rpm for floppy disks). We, personally, have never experienced Zip disk failure, while dealing with dozens of Zip drives. The enclosure of the Zip disk is less open than that of the floppy. Therefore, there is not much that can be done if it suddenly stops reading or writing.

First, try to read this Zip disk using another Zip drive (ask a friend or colleague). Maybe the problem is in the drive, not in the Zip disk.
Blowing air through the opening of the Zip disk may not be a good idea, since the slider / disk interface of the Zip drive is more delicate that that for floppy drives. If the data on the disk are valuable to you, do not try anything else and contact professional data recovery services.

Magnetic hard drive

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CD, CD-R, CD-RW,and DVD

If you have problems with reading the CD, it's mirror surface could be contaminated by particles, fingerprints, various stains or, unfortunately, scratched.

To clean your CD use a soft lint-free cloth and apply light strokes in the radial direction only! The data on CDs are stored and read in a circumferential direction and the drive's optic is less sensitive to radial scratches you may generate yourself!
Data on CD disks is protected by a layer of lacquer on one side (mirror side) and by another layer of polycarbonate (PC) plastic on the other side (label side). The data are stored in the form of shallow pits in the PC matrix covered with a thin reflective layer of aluminum. If you scratch the disk and this scratch is deep enough to damage (remove) the pits, your data is lost locally. Fortunately, CDs are robust and not all scratches cause irreversible damage. If you have scratches on the mirror side of a CD and you really want to try recovering the data yourself (instead of looking for professional help), then, there are a couple of things you may try.

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Try polishing shallow scratches away with mild abrasives (i.e., toothpaste or furniture polish). Clean away the residue. Use radial strokes only!
Try to use fillers for deeper scratches (furniture wax, car wax, etc.). Cover the entire surface and buff out using clean cloth. Again, use radial strokes only!
Try to copy or duplicate the damaged CD as soon as possible.
WARNING!!! Damage to the label side of the CD could be even more dangerous than to the mirror side (sometimes)!

Magnetic Tape

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Data recovery services

In case of data loss or damage to your storage media or drive, do not panic and do not try to fix the problem immediately - you may destroy your last hope yourself (for example, by repeatedly restarting your hard drive hoping that it will finally boot-up in spite of that squeaky sound coming from the inside...).