Computer automatically restarting!!

Hello,

I'm having a really strange problem with my computer. When I turn it on, my monitor registers that the computer was turned on but only for about a second. Then my computer instantly shuts down and restarts. When it restarts, it ignores all devices attached to it, including keyboard, monitor, USB ports and such.
I have tried resetting the CMOS by taking it out for about a minute and putting it back in. Others also suggested to move the jumper pin to another position but there is only one position.
I don't think it is a heating issue because the computer restarts almost instantly. Literally, it restarts within 5 seconds.
Any suggestions? Thanks