need help...really2 need help here...

my pc problem :
when i'm playing dota or cz, about 20-25min, my pc hang!!but my pc never hang when i'm playing other games like cod4,tiberium wars and hellgate london..i cant do nothing xcept restart my pc..then after restart, at the bios, an error occured--->'overclocking or overvoltage failed'...but i never try to overclock my pc..anyone,please help me.