Your hard drive may be bad.
However, what has happenned is that one or more files in your Windows folder are corrupt.
Start by booting from a floppy (Windows startup disk)
If you don't have a startup disk, go to www.bootdisk.com, and downloadthe versions for your OS.
Then, re-install windows.
Make sure that you set the install folder to C:\Windows (unless you installed windows in a different folder)
That should fix the problem.
Then, run scandisk in thouroug mode to give the drive a good check, if there are a lot of errors, I would start backing up files, and buy a new drive.
Chas