computer unexpectedly restarts. SDRAM Related

[Improperfaction]

ok, so i get this new chip of sdram. ULTRA DDR Memory 512MB PC3200 DDR 400 MHz. I plug it in to my computer and it works fine for the first few hours. then randomly, some wierd blue screen flashes for about 1 second (not the blue screen of death, i have windows XP SP2) and the computer restarts.
After that i try logging in to my windows sign on and it does the same thing again. I took out the new chip and it worked fine, but if that chip is in, it will restart itself about 5 seconds after i log into windows.

I know quite a bit about computers, and i have never encountered this problem before. if you know anything about it, pleese help me.

-Improperfaction

 

[Ste]

Download Memtest 86, burn to disc, boot off of it let the tests run for some hours.

 

[Improperfaction]

Download Memtest 86, burn to disc, boot off of it let the tests run for some hours.

hmmm what does this program do? Im big on computer security and i need to know what it does.