What operating system is it? Windows XP?

I know there was a way to disable bad sectors in FAT filesystems, using Windows ScanDisk. I don't know about NTFS, but there's probably a way. Try the utilities on the Windows CD (if you boot from the CD you'll be able to get to a repair console). If your computer did not come with a Windows CD, you should call the technical support of your manufacturer.

If you have a spare hard drive, you could just back up your important files and reinstall Windows on freshly formatted drive. You can do this most easily (the backup, not the Windows install) with a Linux LiveCD distribution such as Knoppix. You may also have more luck accessing your drive through Linux - it seems more able to work around problems than Windows. If you have a normal Windows CD, I'd recommend doing this (reinstalling after formatting) anyway to avoid the extra rubbish that manufacturers place on their computers.