upgraded my pals system to 7 earlier but i got the BSOD with the machine check exception, i then started again and again and kept getting the same prob

took the machine up2 pc world and they ran a 10 min diagnostic and said all hardware was working fine but the cpu fan was dirty so splashed out a tenner and got some air and gave it a blow out

started up the install again and it came up with the same BSOD

then went back to installing XP and it came up with the same

ive also took out one of the ram sticks and tried it but it kept doing the same

any clues?