It seems the place to start would be the power supply. Do you still have the old one?
I would say try the old supply. It should boot the system, or at least show you video. Also make sure your video cable is seated all the way.
You may have a bad power supply.
Hi guys. I recently bought a gigabyte 990 xfa ud3, I installed it and worked perfectly. Since I wanted to replace my psu I bought a thermaltake tr2 750x rx, but after placing all the components and turning it on it didn't show any video, yet the video card fan was on, same for the cpu and the rest of the case fans.
When I installed the PSU I noticed that the plugs weren't as neat as my previous one, actually the 6 + 2 12v plug didn't fit in, so I had to use the 4 + 4 atx 12v connector. Shall I try to unplug everything and then try again?, shall I try to take the board's battery out?, Anyway I am pretty sure there wasn't any short circuit and that I didn't for the video card. What can it be?