Memtest86 Testing Error

Everytime I try to scan my DDR2-800 GSkillz memory, the top part turns black and it freezes, but it also gets through XP Pro SP2 setup fine... what's going on?!

Overclocking too much, lack of voltage or too much voltage, heat, overly-aggressive timings and an incapable/aging PSU can all cause memory errors. List specific version of Memtest you used and which# of test(s) + the error codes.