what could cause my computer to turn on and off repeatedly when I turn it on?

All kinds of things - which makes those type errors difficult to troubleshoot. Some causes are bad CPU, bad RAM, bad PSU, bad graphics card, bad motherboard or just about anything else connected to the motherboard. I usually start by ensuring I have good power by swapping in a known good PSU. Then I might remove all but one stick of RAM, make sure the interior is clean of heat trapping dust, and power up and make sure the CPU fan spins.