In most cases its not a virus. What I whould do (and it sure works) is reinstall windows 98. But before you reinstall:
Make sure that all hardware work fine check all the fans (the fans are the hardware that make windows act up) make sure that whenyou close the box the CPU fan is not getting blocked by a cable. Start by removing EVERYTHING connected to your computer, except for the HardDrive (HD), Keyboard, and VGA (remove even the mouse). If its starts normally, then reconnect one device at a time and see if the problem comes back (start by the mouse, then the Floppy, then the CD-ROM, then the Sound card, then the Modem, then the NIC, and so on) restarting the computer as you reconnect a device. Some times it can also be the P/S. Try starting your computer in safe mode. If it starts in safe mode, and you can run programs without a problem, (except that the color isnt good) than its a hardware device (other than the fans) thats making problems. If nothing helped, your windows needs a reinstall.