Several more troubleshooting steps:
It sounds as if for one reason or another, Windows has become corrupted and may need to be re-installed after backing up your sensitive data - (Internet Explorer Favorites, Netscape Bookmarks, Outlook Express contact lists, letters, pictures, databases, spreadsheets, music, etc.) to removable media for restoring later. But first
Update your antivirus, temporarily disable your screen saver and scan with your anti-virus set to scan All Files. Update and scan bi-monthly. Create your anti-virus' Rescue disk(s) and update them after each Windows anti-virus update.
You can scan on-line to double-check your Windows scanner at
http://housecall.antivirus.com
Get free Zone Alarm personal firewall anti-hacker countermeasure from
http://www.zonelabs.com. (not the demo) Don't let anything out to the Internet you don't know what it is.
Cure Your Ills With the System File Checker
Windows 98
When you're having trouble with Windows 98--and who doesn't at some point--you might want to try a little-known utility called the System File Checker. Close all open programs and go to Run in the Start menu. Type sfc and click OK.
Check the Scan For Altered Files radio button and click Start. SFC will look for files that have been corrupted. If it finds any, you can use it to extract clean versions of the files directly from your installation disk.
Or
To start System File Checker, follow these steps:
Click Start, point to Programs, point to Accessories, point to System Tools, click System Information, and then click System File Checker on the Tools menu.