Sudden Laptop shutdown !!

Hello,

I have a TOSHIBA satellite & it was workin fine until recently....then it started to shutdown whenever I play any game on it...first I thought it was a heat problem but I kept monitoring it with a software called NHC (Notebook Hardware Control) & I noticed NO OVERHETING whatsoever (the max heat it reached was about 66 C)....I tried to unplug the battery & work on AC power no use, thought I have a Virus so Formatted the system but no use (& I have an excellent anti-virus software)...now I really dont know what to do !!! ....could it be a RAM issue !?

I have Windows VISTA (which sux big time)

ur help is seriously appreciated
Thank u