Could be heat related the newer computers will shut themselves off, are you sure all fans were operational specially the CPU fan. Did you put the CPU on the board yourself? If you did are you sure it's seated right and that you used good quality thermal paste? Have you tried unplugging each of the audio cables and rebooting? I'm no expert for sure but imho it sounds to me like the mobo is cooked. I"d wait tho for more experienced people to drop by and add their input.
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