problem :s

Hi
i have a problem when i start E.T or another game after a 10-15 mins my pc reboot alone ; ..
Pc reboot when i start E.T or he send me a error message without rebooting or i can play but graphics is shit :(( ..
i want know what is the problem with my pc for fix it ..

Maybe i need to change that : http://www.ominfo.com/bases/uploads_dedie-ipt/1074865372_photo1_alimpc_1.jpg or what??
Help me plz , thx
(soz bad english)