Go back to what worked.
Some PCs DEMAND (as in not optional) that the BIOS be current to accept a CPU on the machine's CPU SUPPORT LIST. But here we have no make, model and BIOS version to work with.
I recently bought a new cpu from the store, and when I plugged it all in and turned the computer on, all of the lights and fans worked, but nothing showed up on the monitor. If there is anything I can do, please tell me. Thank you