i am putting together random computers but i put one together everything is connected right but it resets itself and doesnt boot

Probably not enough power supplied from the PSU.

Had that happen at my job once. Our theater ad servers backup battery malfunctioned and used up its battery to power the server. Eventually, it had only just enough power to turn the thing on, but not enough to sustain it, so it kept turning on and off untill eventually it killed the CPU's.

i got it to work finnaly