Memory causing freezing.

Ok so i overclocked my computer using this guide http://www.neowin.net/forum/index.php?showtopic=503808http://www.neowin.net/forum/index.php?showtopic=503808 and afterwards my computer started to freeze every ten minutes or so. I changed the ram to a 512 stick i has lying around and it stopped freezing, so ive come to the conclusion its the ram. I then put the good ram i had back in and it continues to freeze. I put on of the sticks in and it went longer, but still froze. any insight on how to fix this would be great!!!

oh my memory is. 2x CorsairCM2X-6400



E6400,2gig corsair ram, 1950xtx, Thermaltake Typhoon cpu cooler, HIPRO 600w PS.

I cant even run a memtest cause it freezes.