Pc keeps crashing

Sep 26, 2018
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I have amd Fx8320e with gigabyte ga-78LMT-USB3 ,8GB RAM and r9270x gpu and 650power supply . My PC started crashing (not windows crash with blue screen but directly freezes for a second and restarts).then I removed my gpu and triedbut still it crashed then I installed Ubuntu thought windows might me the culprit but no success It crashed in same manner .I flashed the bios with latest update(wich was dated 2015or 14 ).
And vola it started working like new pc .but for few days and again same problem . As I kept the pc off for more time it would stay on for longer time and eventually crash .also tried with 3 power supply and currently I have Installed newone (borrowed for a friend ) no success.
I also contacted a guy who repairs motherboard but he was not an expert he said he can't help (he only suggested me to update the bios


I need to know if anyone encountered such problem and what was the culprit or solution. I can't afford to spend any money on replacing any component .It would be very helpful if anyone knows whether the bios chip is faulty of power delivery chip is faulty or any other chip.