Question Reboot loop and black screen

Mar 30, 2020
I'm stuck home due to the outbreak and my dad's old pc stopped working. It runs for ~15 minutes when I turn it on and then it reboots, and keeps rebooting every 2 or 3 minutes after. I reinstalled the system but the problem persisted so I guess it's a hardware issue. I'm trying to identify what exact part is broken but my options are limited due to the situation (I don't have spare parts here to test).

What I've noticed today was that after 4 or 5 restarts, the monitor turns off and it stops rebooting (I can hear the fans running but the screen is black), so I'm starting to think the graphics card might be overheating and shutting off? Does anyone with more insight knows what might be the problem?

Edit:It just rebooted again after 45 minutes of no signal to the monitor. I have no idea what to do.