Welcome to TechIMO.
I would suggest doing the following.
Go to the online anti virus scanning site: housecall.antivirus.com
Do a full scan of your hard drive. If no viruses are found, get a free anti virus program. I recommend AntiVir. There is a free version for home use at
www.hbedv.com. I use it on all my systems and it works great.
Now I recommend going to:
www.lavasoftusa.com and download a program called AdAware. Install it and run it. It will look for Spyware and other malicious code that shouldn't be on your PC. The go to
www.safer-networking.org to download Spybot Search and Destroy. It will look for some Spyware that AdAware doesn't see and vice-versa.
If that comes up clean then I suggest reinstalling your PC from scratch.
Backup any data and then format and reinstall Windows 98.
After you've done that go to
www.zonelabs.com and download ZoneAlarm. It's a personal firewall program that helps protect your PC from being broken into from the Internet.
Sean