random blank screens!

blank screen will show up at any time 2-5 seconds later the system will stop responding. system also freezes(normal screen) but mouse still operates then freezes also after a few seconds. also freezes during windows user logon.

i have an abit ka7-100 mobo, athlon 950mhz, 256MB SDRAM, ati all-in-wonder Radeon 32mb graphics, running WIN98