Question Two Computers Turning Off and On Repeatedly ?

Jan 12, 2021
Hi. I am helping a friend put together a new PC. When finished, the computer began turning on for 8-10 seconds and then restarting and repeating that. No beeps, no display, but fans and lights running.

So, I try and narrow down the problem. I remove the graphics card. Same behavior. I removed the RAM. Same behavior (should beep, right?). I have checked all connections multiple times. I guess that leaves the mobo, cpu, or psu.

So, I went and got my psu which has even greater wattage and worked as of 2 hours earlier. With only the psu switched, same behavior. So at this point I was thinking it is definitely the cpu or motherboard. Then, imagine my surprise when I put my psu back in my computer and start getting the same behavior on my pc as the new one!

First question: is it possible that someone this troubleshooting has ruined my psu?

Second: Can someone tell me what would cause this behavior and/or give further steps to troubleshoot? I am pretty much out of ideas.