I have an AMD Athlon 64-X2 4400+ processor on Gigabyte GA-M61SME S2 with 3Gb kingston rams and ATI radeon HD 2600 XT. After I play any game for some extended period CPU heat reaches 100C degrees and computer just powers off. It never happens outside games. I tried to change the heat-sink, the termal paste and even the power supply. I tested my CPu on another computer and ran World of Warcraft, which my friend's computer cannot run with full graphics and his computer worked just fine (in fact my friend changed his cpu to match mine to get improved performance and he has no problems. I'm highly suspicious of mother board and/or my graphics card. How can I find out where my problem is and is there any alternative component that can cause the problem?
Well, did you use a pea sized drop of thermal paste and made sure that it was mounted correctly? Also, what power supply do you have? I doubt motherboard has any influence on the CPU temperature, which is why I'm ruling that out if it still turns on and can boot into Windows.