R9 295x2 - No display

[Nyestuer]

First of all, I'd like to say that I've read tons of thread just like this one, but I just can't get it to work.
I built my first computer yesterday, and everything was working great, until I figured out I had my motherboard connected to the monitor instead of my GPU. The GPU's leds are lighting up, and the fan on the radiator AND the gpu itself is spinning.
I tried connecting the monitor(and other monitors, using DVI cable instead of miniDP) and it's still not working.
The graphics card is NOT shown in Device Manager.
When I try to install AMD - Catalyst I get the following message: "Application Install: install package failure".

So I googled it, and I've tried:
Checked all the power cords and making sure the GPU is correctly inserted.
Using another PCIe slot.
Updating BIOS (I have the newest version.)
Resetting CMOS
I have tried setting the PCIe as primary in bios, but it just goes back to auto.
Uninstalling ALL display drivers from Intel/AMD, and then try to install AMD Catalyst.
I've also tried the above but in SAFE MODE.
AMD AutoDetect
Windows Update

I'd really appreciate any help, been trying for 8 hours straight.
Thanks in advance!

 

[clutchc]

The card may be defective. Or your PSU may not be sufficient to power it.

 

[Nyestuer]

As embarrasing as this is to admit... turns out one of the PCIe power cables was not plugged in all the way into the PSU.

Had been trying to fix this for 9 hours before I gave up and went to the gym. In the shower back home I suddenly thought of the fact that I had only checked the cables going into the GPU.
Thanks a lot for all the help clutchc, even though it was just a redicilous mistake on my part.

 

[clutchc]

No prob. Happens to all of us. Enjoy.