I have this issue trying to get the best direction.
My computer randomly has hard shutdowns fans go to 100% on graphics cards sound go crazy on speakers and then restarting this comes with no warning or consistency i could run 3 hrs or 5 minutes nothing consistent. graphics cards and everything run fine when operating normally. I know this is signs of a possible bad psu or it could be a failing MB. I have a thermaltake psu 850 watt and a asus x58 sabretooth MB no overclocks on it now. i have 2 gtx 570's in sli
from previos experience what is the best direction i dont have parts lying around and trying to keep it cheap.
I had a similar problem. It was actually a combination of two things for me. One was that there was a bad pin on my fan controller so it was not properly grounded and after any amount of time, build ups occurred and crashed my pc. It can also be static electricity, due to the case not making proper contact with the power supply or even just a static shock to a port (like the headphone jack, or along a badly insulated USB cable) so watch for those as well.