Click and then reboot

I received an iMac with the screen entirely taken off, I believe they tried to remove the hard drive before getting rid of it. In the process they damaged almost every connector from the LCD to the board, at least slightly. With great precision I think I salvaged the connections and the display seems to be working fine. So I put a new HDD in the machine, booted from USB to High Sierra, initiated the install from the first menu that lets you use Disk Utility, install, etc. with no problems. Then it kept randomly turning off and rebooting throughout the install (much more often than a normal install), I let it do its thing overnight to see if it would install. Came back this morning and the country chooser was up on the screen. I clicked United states, then next, and as soon as I hit the next button, the machine clicked, shut off and rebooted. It stays in a reboot loop for a while, and then gives me the country chooser again, and the same thing happens, click... reboot.

Any idea whats going on?

I don't think the semi damaged display cables would cause this to do this.

I reset the SMC, PRAM, Tried different power outlets and cables.