Question Help! Graphics card not working?

[Antoneck]

So, I just bought a computer, used one and then a graphics card separately.
(Z97S Sli Krait Edition
i5-4690K
16 GB RAM
etc...)

And Im using a Radeon RX 570 card.
The guy I bought the card from talked about Flashing bios and stuff like that (Used for mining? IDK)

Now to the problem.
When I run my computer WITHOUT the GPU plugged in, it works fine.
I get in to BIOS, and so on.

Problem is that when it is in, I cant get into bios, I just get a black screen/boot option list doesnt come up.
And when I come into windows, after I installed the Radeon Drivers, I get a green flimmering screen/black screen after like 30 secs..
This is really annoying and I'm thinking the graphics card isnt working? Or do you have an Idea how I could maybe make it work?

 

[Antoneck]

I just had time enough to check GPU-Z and its the same BIOS version as stock. So thats probably not the problem..
Could it be that Im using a TV monitor right now?