How do I recover a corrupt system file if my Windows was pre-installed?

First, let's run through a few possible ways you might get lucky and be able to recover that single file.

• Boot from that recovery disk, ideally into a Windows command prompt, or boot using one of the many Linux "Live CDs". In either case, this should allow you to explore the data on your hard drive.

• Look for a folder labeled "I386" in the root of your C: drive - you may find a backup copy of the missing file there, or in subfolders there. (Other "I386" folders elsewhere on the hard drive are not likely to have this file, though there's no harm in looking.)

• Look for another partition on the hard drive - perhaps a "D:" drive. Many manufacturers place recovery data onto this other partition so that it remains untouched as you use your machine normally. The missing file might be found somewhere there.

• Borrow a Windows installation CD from a friend and copy the required file. It's likely that you'll need a friend with the same version of Windows as you have.

• Even riskier, you can try copying the required file off of that friend's system. Once again, in the case of ntoskrnl.exe you'll at least need the version that matches your version of Windows. In the case of other files, it's quite possible that you'd need the version that matches your machine's make and model as well.

But even if you do recover the single file, it still may not be enough.

What we don't know is why this file went missing in the first place. The common assumption would be a virus or spyware, but perhaps it's something else.

And perhaps more files are missing. It's quite possible that this is simply the first of many.

The really bad news here is that the right solution is to reinstall Windows, from scratch.

And that requires an installation CD.

I would absolutely contact the manufacturer and see if they can provide you with the proper installation CDs. At this point it's possibly even worth it to pay for them.

Failing all of the above, you can of course go out and purchase a retail copy of Windows.

It's a mess. A mess that could have easily been avoided had the machine been provided with a matching installation CD in the first place.

Lesson #1: when purchasing a machine with Windows preinstalled, insist on getting the installation CD or DVD. There are scenarios such as this one where the original installation media is the only recovery solution.

I also want to touch on a secondary statement made in the original question: "I already lost all of my data once and I can not afford to lose it again."

Clearly, then, you haven't been backing up.

If you'd been backing up regularly and thoroughly there would be no risk of losing "all of my data". At worst you would lose the changes/updates since the last backup. How long ago that would be depends on how often you backup, and that should be a choice you make that depends on how heavily you use your computer.

I backup nightly. I'm guessing that most people who use their computers even moderately should probably do the same.

Lesson #2: backup regularly. You'll avoid data loss when, not if, disaster strikes.