PC freezes up frequently…

PC is running Win98(2nd Edition) has 128 meg ram; 6 gig drive; processor is 700 pentIII. I have run every diagnostic I have..scandisk, virus check, defrag (helps some) I have even configured autoexec and config to free up some memory (helped for a while)..but lately this *!*~~ machine is freezing up alot. Any ideas??