How long has it been since you dusted it out?
But before you do anything, is it all backed up? A machine of such age may decide to stop working if you dust it out, clean heatsinks and check the fans.
At least once a day my pc freezes up. This happens when I use the scroll bar and then it locks up.Then the only way to correct this is to press the reset button. I have done all the obvious, scan disk,defrag, virus scan,spyware removal. Any suggestions ? Win. 98/IE 6.0, AMD K-6.