Question Monitor not recognizing PC

[garyknowz1]

I'm having issues with my system. I can get my system to fire up, but the monitor does recognize both my gpu hdmi or my motherboard hdmi ports. I was able to test both the monitor and cables at Geek Squad for free since most of my old computer hardware is in storage out of state. They both worked on their PC. So I'm focusing on the tower now, but unsure how to even diagnose the problem without seeing the screen to test which component is having the issue.I've built PCs in the past, so I'm not a complete novice. But being currently disabled, so not a lot of money to take it into a shop or buy all new components.Any thoughts on how I can find the component having the issue? It's a CyberPowerPC C Series only a few years old but past warranty. Thanks. GK

 

[garyknowz1]

I noticed an additional thing. When I initially start up the PC, about a minute later, the tower shuts down for a second. Then restarts itself, and stays on thereafter. I noticed that the last a few times I was messing with the machine. Still nothing showing on the monitor though. I reseated the GPU and RAM, and cleaned the inside with my static mat and wrist grounded. Just wanted to mention what I've done thus far.