Computer restart itself after 30 seconds, display shows windows loading screen then loops to beginning

Apr 19, 2018
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My cousins 5 year old pc does this restarting loops. I opened case, clean a lot of dust from Psu and other parts. Re-paste cpu and check all the fans are working properly, except Psu which I assume starts after a while.
Start pc, bios shows up, display working, windows loading screen shows up and restart itself in a continuous loop.

Read online that maybe power button failure cause this, so unplug power switch from motherboard and start with a screwdriver but no solution.

Thinking maybe switch Psu or ram?
Which part can be the problem any ideas?

Cpu i5 3th series
Psu unbranded
Gpu some old nvidia