Random freezes. CPU or motherboard?

[AmyTheBun]

Long long ago, My old PSU killed my GPU and HDD in a power spike, every since then I get random freezes where if my pc was playing a sound it'd just keep on buzzing loud and just i couldn't even use the restart button on my case. the only option was to hold the power button for a few minutes. I've tried everything and I checked my RAM for faults with a software (I forgot the name of) but it's apparently okay?

 

this happens on a fresh windows install too and happens without a graphics card and also happens in Ubuntu and not just windows. It happens once or twice a week.

 

so I'm 99% sure its either my motherboard or CPU. but how do I know which one it is? I found a 3770 on a website for 60$ so i was gonna try and see if it helps, any ideas if i should? how do I tell which one it is? (my motherboard is a p8b75)