need help!window install

yesterday,when i was surfing the internet,my computer turned off automatically(the power was off).i thought maybe my windows2000 system was not so good or maybe some virus ).so i formated it and installed again.but my computer cann't install windows2000.and i changed to set up window xp.but it cann't installed either.(the problem is that when window is installing on the hard disk,(the files have already copy to the hard disk)my computer will turn off automatically,in the same place)anyone knows what is wrong with my computer.i had checked my hard disk is good.and now nothing is in my computer.please help !