Take a look at the motherboard manual and see what memory it needs. My computer used to reboot whenever I tried to do a render with too many Millenium 3 characters in a scene. The only thing I could figure out was that I was using PC2700 memory when the manual said my motherboard took PC2100 memory. Shouldn't have made a difference... but when I got the PC2100 sticks, my problems went away.