Imagine the following scenario: You turn on your Windows PC, and calmly watch as the BIOS performs its normal memory and device checks. But then it stops far too early, and reports "Invalid system disk", or "Disk boot failure", or a similar message, depending upon your BIOS. In other words, the boot sequence has stopped dead, as has, most likely, your breathing.
Contrary to what many people believe, this is not a problem with the operating system (a nice change of pace), which would give a quite different error message if it were unable to start. For Windows, that is usually the infamous "Blue Screen of Death", which adds insult to injury by providing some of the most useless error messages of any major computer application.
If you see a message informing you that a system disk cannot be found, do not immediately assume the worst. Chances are that someone (we're not naming names) accidentally left a non-bootable diskette in the diskette drive, and the BIOS is set to boot from the diskette drive before any hard drive. In that case, simply pop the diskette out, and press the Enter key if your BIOS is prompting for that, or the Reset switch otherwise or if pressing Enter does not work.
Note that this event is the most common way for computers to become infected with boot sector viruses, which, fortunately, are much less common these days. Nonetheless, if your PC did try unsuccessfully to boot off of a diskette, then you are not completely out of the woods. The first thing you should do after Windows has finished starting up, is to run an up-to-date antivirus program to confirm that the boot sectors of any of your hard drives have not acquired a virus from the diskette.
In addition to the dangers of a boot sector virus, there is another reason why your BIOS should not even be trying to boot off the diskette drive. If you are using a more recent version of Windows — such as XP or 2000 — and you need to install or repair a Windows installation, you would boot off of the Windows CD anyway. Thus, you can speed up your typical boot process by having the BIOS not try to boot from diskette. If you feel comfortable changing your BIOS settings, then you can change the boot sequence so that it first checks for your primary hard drive, possibly after checking the CD-ROM drive.
Now You Can Panic
But what if you check the diskette drive and it does not contain any diskette fully inserted, or the boot sequence is not set to check the diskette drive? Then this means that your computer tried to boot off of your primary hard drive, and it failed. The situation usually goes downhill from this point, because either the boot sector of the drive is no longer working, or the entire drive is dead.
You may be wondering how a hard drive could fail. After all, isn't it just one of many components in your computer, which rarely if ever stop working? When was the last time you heard of a motherboard, or a RAM module, or a network card simply giving up the ghost? Hard drives are different, largely in that they have moving parts. In fact, the most reliable components in a computer are those that are solid-state, with no moving parts. In contrast, cooling fans, optical drives, diskette drives, and hard drives suffer the bulk of the failures.
What causes hard drives to fail? Excessive heat, vibration, or shock; moisture getting inside; or simply failure of a critical part. Hard drives fail more often than most people seem to suspect. In fact, inexperienced computer users typically express shock and disbelief when it is pointed out to them that, without backups, they could lose everything in the blink of an eye. Wise computer consultants caution clients that they should consider it a matter of not if, but when, their drives will fail, taking all of their critical data to the big Recycle Bin in the sky.
Cluster's Last Stand
So what do you do if and when you confront the computer user's worst nightmare, a hard drive failure? If you feel comfortable working with your PC's innards, and perhaps have some experience replacing said innards, then open up your PC, reboot, and listen to determine whether your hard drive is even spinning up. If not, then there has been a mechanical failure within the drive, and you will have to purchase a new one.
If the drive in question does spin up properly on boot, without making any suspicious grinding or clicking noises, then it is probably working fine mechanically. It is possible that only the boot sector is not working. In this case, you should boot off of your second drive, if you have one. (This is one of several excellent reasons for having a second hard drive in your computer.) Then try to repair the master boot record on the bad drive. For most versions of Windows, the command would be "fdisk /mbr". Note that fdisk is a powerful and thus potentially dangerous utility, not to be taken lightly.
If the master boot record is beyond repair, then see if you can at least read your personal and other valuable files on that drive. If you can, copy them to your second, working drive (another handy use for a second drive). Do this as soon as possible, preferably before any reboot, because when that primary drive starts to fail, it can go quite quickly, and then you will regret not having taken advantage of that chance to save your data. I know this from painful experience.
Call in the Cavalry
If you are unable to read the files on the failed hard drive, then all is not lost… well, perhaps not. It may still be possible for the data to be read from the hard drive's platters by data recovery specialists. These are companies and individual consultants who have the equipment, expertise, and experience in reading seemingly unrecoverable data off of hard drives that have failed mechanically, or that have been damaged by fire, water, and even bullets. These are the same folks who assist law enforcement and intelligence agencies in recovering incriminating evidence from computers whose owners thought the files had been deleted permanently.
However, there is no guarantee that the recovery experts will be able to restore your valuable data. In addition, successful retrieval of your data could cost you several hundred dollars. On the other hand, do not entrust your hard drive to the lowest bidder simply based upon price. You don't want to be the guinea pig for someone getting started in the data recovery business. In that field, like so many others, experience, track record, references, and confidentiality are worth every penny.