I'm not in the US btw

I had a look at a few stores and they're all pretty expensive.
I'll rather look for 2nd hand components. It'll be much cheaper to replace both the CPU & the mobo than replacing the faulty component at the tech store (and I can sell the working components afterward anyway).
Plus, there's still a chance to get the right component the 1st time.
Here are the facts again, tell me which component you would try first :
* bad o/c : raised the CPU frequency too high with BIOS on auto voltage
* fried a PCI sound card in the process
* now the computer shuts down by itself when watching movies but not always. Usually it'll shutdown once and if I restart it and go on watching it'll work fine until say the next day. Some days it won't shutdown.
* it also shutdown once using Pinnacle Studio (videomontage app). I think the common denominator here is video playback.
* tested all memory sticks one by one
* installed a new OS
* cleared CMOS