issue display

Hello everyone, I'm having an issue where my PC is no longer showing any display. This happened after I had decided to replace the thermal paste on the CPU. I've done this plenty of times before with no issue but I'll admit I did rush things this time around. After I put everything back...

To begin with, please understand that I cannot afford more and I hope I won't be judged by what antiqitues I run. I used to have an AMD Radeon HD 7850 2gb on the exact same setup as I have now, but I have bought and installed an AMD RX 480, the 8gb edition, Spahire Nitro to be more specific...