Computer turns on then back off in a loop

Computer was running fine when I shut it down but when I restarted it it was in a loop cycle of running for a few seconds and shutting off. It was not making it long enough to light my keyboard up or get to the bios. I unhooked everything but the cpu mobo and psu and still did the same. I also cleared the cmos and bios at this point. A friend told me to just use 1 ram and try to start it butand it didn't work but it ran lknger. I turned the power supply off with the button on the back instead of unplugging it at this point and we n I restarted it went to the reset bios screen. I set the bios up to the profile I had before I reset it and when it reset it back to the loop cycle. I tired the psu off from the back again and it restarted and is still running but I'd like to have my other ram stick in and would like to find out what caused it to begin with. Anyone have any advixe? Please and thank you