Hmmm, windows 98

If you have had your computer for a year or more, backup all your files and format your harddrive. I've found out from experience, that formatting and reinstalling windows will clear up almost any problem you could have. It's like starting from scratch, but you will be sure that you got rid of any malicious files that would cause your computer to be messed up. You probably will save more time by just erasing eveything and reinstalling, than getting frustrated by not being able to fix your computer.

And do what Nimrod said. 98 is get XP if your computer supports it. Many enhancements over 98. Also, If you decide to do this, format your harddrive to the NTFS file system. You are currently using FAT32 now. NTFS is MUCH faster and will give you better overall performance.