Hi
Can you boot into Safe Mode? Press F8 when the computer starts up and select Safe Mode from the Boot Menu. If Windows starts in Safe Mode run System File Checker by clicking Start>Run and then typing
SFC
in the Run dialog box, then press Enter. This program will check your core system files and offer to replace any that are corrupt. It will also notify you if there are any later versions of a system file available. You will need your Win98 CD or have access to the CAB files from the installation CD's Win98 directory (these are sometimes copied to a hard drive).
Also, if this does not work, you can run a repair of the OS without losing your settings and data. Again, you will need either the original CD or acess to the CAB files to do this.
Good luck