My computer is turning on, then shutting back off again. I checked all connections, verified all cards, ram, etc was well seated. Everything seemed to be fine, so I replaced the power supply. It seemed to work better for a few minutes, and went right back to shutting off. I'm not getting any beep code. I'm trying to determine if there's anything that could be causing this except the motherboard, or if it's time to give in and replace that too. Can anyone suggest additional diagnostics, changes, etc to look for?
Have you tested with the board outside the case? If yes and still the same, then it looks like a motherboard issue.
Try though reseating the CPU and reapplying thermal paste. Use the stock cooler for testing if possible.