need help PC gets power, won't boot.

[J. Wick]

PC powers on but won't display anything on the monitor.

Previously, the 24-pin cable from the power supply to the motherboard was too short, so an extension cable was ordered. Was not the one to order it so I'm not sure if the extension cable was third party or not. 

Previously, the PC would boot into the BIOS however when told to boot to the flash drive with Windows 7 on it, would restart and go back to the BIOS. Same result with flash drive that has Windows 10 on it.

After rewiring everything, the PC doesn't display anything to the monitor when turned on, can't tell if it's booting into the BIOS or not. 

PC restarts on its own every 10 seconds. 

PC is using VGA cable to connect to the monitor.

PC does not have a graphics card or HDMI ports.

So far have tried swapping RAM back and forth, inspecting internal cables, and swapping outlets. Had two people who know a thing or two about computers take a look, did not find the cause of the problem.

Can provide more information if necessary.

Edited November 13, 2019 by J. Wick
added more information about troubleshooting