My computer wont stop cycling

MixedApril Posts 1 Registration date Saturday December 11, 2021 Status Member Last seen December 11, 2021 - Dec 11, 2021 at 10:12 PM
My boyfriend decided to change the cpu on his pc and replaced the cpu fan with the new cpu. His old cpu has bent brackets so it was a good idea to switch to an upgrade. But when we plugged everything back, the computer turns on for exactly 30 seconds (nothing appears on monitor) and then turns off for 1 second and then the cycle repeats. I have unplugged everything, the ram, gpu, cords and switched the power supply but there is nothing that stops it from cycling over and over when I start it. I'm thinking its the motherboard, but it turns on and the motherboard is compatible with the cpu. What could be wrong with the pc?