Help thread, my pc randomly shut down.

Aug 10, 2018
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Pc specs
i7 2600k
GTX 1050 2gb
I don't know the motherboard at the moment, probably some old gigabyte motherboard from 2012 though
some random wd harddrive from 2012
stock cooler from 2009
Ok so since I got my computer my CPU has been running at 60 to 70 on just by doing normal stuff like watching youtube, I know it is abusive to keep my CPU at those temps but I bought a cooler and it is supposed to come in a couple of days.
Today I was watching some youtube as usual when all the sudden my pc shut off, no turning off screen, my monitor just went black and my leds shut down so I try to boot it back on again and everything goes fine, my hard drive is even spinning but after the bios screen my hard drive just shut off again and the same thing happened. I have tried to turn it back on multiple times but still the same. If someone could please tell me what is wrong with my pc I would appreciate it, I am willing to buy new parts. Sorry for terrible English, it is not my native language. :D