Question System has Power but No Post or Display

Sep 15, 2022
1
0
10
I bought a Dell Optiplex 990 the other day. The system has power but doesn’t show a post screen or a display output. The display port detects something is connect but nothing else. There is no beep codes or led error codes as well. Any suggestions?

I have tried
Clearing the CMOS
Reseating the RAM
Swapping the RAM for a different kit
Adding a graphics card
Taking the entire system apart and put back together