PC repeatedly boots for half second and shuts off

Jun 25, 2018
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I have had this PC for about 2 years, finally decided to upgrade graphics cards and installed today. Was working perfectly for several hours after which the pc completely froze while browsing the internet and now won’t boot up.

The fans spin for half a second and shut off, this repeats until I turn the power supply off. Occasionally, the pc will boot for a few minutes before freezing and getting stuck into the loop.

I’ve tested the psu with the paperclip test and it works fine. Removed the graphics card (also tried the old one) but had the same issue. Not sure where to go from here and would really appreciate some help.