What version of Windows is on it? Does the drive show up in the information screens when your machine is first powered up? (The POST screens of information during the checking stage, before Windows starts to load)
Do you have the Win98 CD? Try to boot from it. Don’t know how this will help you, but you can Maybe reinstall Windows if you don’t mind lOOSING your DATA. I have never done a repair with Win98 don’t even Know if it’s possible but maybe that’s what you should be trying to do.
If you have another machine you can put that hard drive in that machine and hopefully recover any vital data. Then put the hard drive back and reinstall windows.
These are just some options and are really, only good if your hard drive is not dead.
If your drive is detected during POST but doesn't appear as a system disk, then either the boot sector on the hard drive is corrupted or the system boot files are missing or corrupted. You'll find a reasonably good guide to troubleshooting the situation at:
You'll need a Windows 98 Boot diskette so you can boot from your floppy drive, and if you haven't got a woring one there then make one on a friends Windows 98 system, get your local computer shop to make one for you if they're friendly enough, or download the necessary boot diskette image from: