Failing to boot BIOS

[Slynet]

Hey. So last night I took off my default backplate to fit the custom one that comes with the Noctua NH-D14, then put it all back together and now the PC fails to boot. I can't even get into my BIOS, nothing is displayed on the screen, no sounds are given from the motherboard. All of my fans are spinning, the HDD is spinning and the optical drives sounds like they're working, but nothing is displayed to the screen, as if nothing is connection. I have a ATI 4870X2, none of the red diagnostic lights are showing on the back of the card. I don't have a clue what's wrong with it, I've double checked all my cables and even rebuilt most of it.

Main components:

ASUS P5Q Deluxe
Intel E8600
Noctua NH-D1
ATI 4870X2
4GB Kingston HyperX
Coolermaster 620w Modular PSU

Any ideas why it might not even be reaching the BIOS? Cheers.

 

[Slynet]

When testing the motherboard outside of the case, is it OK to test it purely with the PSU connected to the mother board and graphics card, and with my CPU cooler connected up, nothing else? On a wooden surface of course. Is it OK, in that, will it at least display the BIOS, or do I have to have the HDD and other components connected?

If so, I just did this and it still doesn't work. So either the CPU cooler isn't installed correct or something is damaged; which I'm hoping is not the case though.

I had the speaker plugged in correctly before, no beeps were given out though.

 

[Slynet]

So after swapping and testing everything, I've found out it's two of the RAM slots that stops it booting; regardless of what cooler I'm using. The RAM itself is fine, I can swap them with the two working slots, but if I put any RAM stick into the two broken slots it will not boot. I don't what I have done to cause this, I didn't even really touch the RAM.

Is there anything I can try to get these working?