Come to think about it, i would now think that its a Motherboard problem, my last motherboard was faulty and whilst my PC booted and worked, it randomly shut down and in games too even shorter time to shut down, and i replaced the whole ocmputer except for the mobo before finding out it was the Mobo.

Buy a new shuttle barebones could be the best option, but maybe just a new motherboard? i guess its using a micro ATX right?