Windows

It sounds like you have registry problems and / or corrupted system files.

Did you transfer Windows from an older machine?
Even if the old mother board used the same make chipset, you could be experiancing device driver conflicts.

Are you over-clocking? This can also cause weird system problems.

Have you checked for viruses? This is always good to check when the system starts acting weird.

Check for conflicts in device manager, correct them first.

My first thought is to back up your data, format the hard drive and start over.

You might be able to recover using a good system utility such as Norton System Works, or Fix It.

Either way, make sure you have the latest drivers for your mother board and plug in cards.

You also should check your BIOS settings. In particular, some video cards require having an IRQ assigned, others don't.

When you install drivers, install the chipset drivers before those for the cards.

There could be a program that is causing the system to hang
It can be caused by Screen Savers running in back ground or a program that is not responding,when you see the message,hit the CNTL+ALT+DEL keys simataneously and you will see the program that is not responding you can then hit end task
To fix this you can Open the Control Panel,double-click the Power Manage icon and uncheck the box to disable and reboot

Sounds like a general instability.
I would start by checking CPU voltage settings and system temp. If it is overclocked i recommend that you step it down a bit to see if it stabilizes.
Technical documentation on AMD CPU:s at:
http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_739,00.html
Be sure to remove any spaces or % in link.
HTH
Tom

Your hardware is enough to work under win98, but for some "Microsoft" reasons, the time to make a fresh win98 install, has arrived.
The very first move will be to backup (or copy to another partition, those important files (if you have one!))
Thenmake a floppy boot disk and copy to it the necesary files in order to make your system works under DOS.
The format your c: drive and install there a fresh copy of win98.

Hope it helps!!

Do you have any antivirus software on your machine? If you don't. Get it. Make sure your virus definition files are up to date and then do a system scan. You want to eliminate the possibility of a virus first.