No video output after case switch, fans spinning

[plzpuddngplz]

I just swapped the family's computer from an NZXT Gamma to a Bitfernix Merc Alpha, and after moving into the new case, I get no video output, but fans are spinning, seemingly like during a normal boot.
The computer worked perfectly yesterday, before the case switch, and nothing besides the case has been changed, hardware and software-wise

As you might have guessed by now, the computer isn't booting properly. It seems to be booting up normally (fans, HDD spinning), but will not output video. Also, the first time it boots it wil run normally (still without video) for a few seconds before turning off and restarting.
Below is a list of all the things I've already tried. It might be useful to know that I did reapply thermal paste to the CPU while doing this, but nothing else was removed or fiddled with.
This is the first time I've used Intel's push-pin system as opposed to AMD's solution, and as such might just be an error on my part,but I've checked to make sure all the pins are in, so I'm pretty sure that's not the problem..
Also, the motherboard I'm working with has absolutely no documentation on which pins front-panel connectors go to, so I figured where the power one goes through trial and error, and will figure the rest out after I solve this. If there's some sort of standard for this, a link would be appreciated. I'm currently taking out the motherboard to make sure nothing's stuck behind there and digging out a system speaker. I also have parts to swap out, but would rather not.
SPECS:
CPU: Intel Q5200
MB: Acer-branded LGA775
RAM: 2x2GB Kingston KVR 1333MHz, 1.5v
CPU cooler: Stock
Nvidia Geforce 8600 (tried to boot with both this and integrated)
PSU: 500w OEM, can't find any other info on it
HDD: Seagate 1tb
OS: Windows 7
Case: NZXT Gamma- Bitfernix Merc Alpha (current)
ANY other parts. If you have an ipod plugged in, we want to know.

THINGS ALREADY TRIED:
1. All the steps here:
http://www.tomshardware.com/forum/261145-31-perform-steps-posting-post-boot-video-problems
2. Different monitors, cables, both integrated and discrete graphics cards, including integrated with discrete removed,
3. Going over all cables (including 4-pin CPU power) to ensure they're connected.
4. Checked with the NZXT Gamma front-panel connectors to make sure nothing's happening there.
5. Re-checking the CPU cooler to make sure nothing's suspicious there
6. Swapped out parts, problem seems to be motherboard
7. Getting a LGA775 motherboard to troubleshoot with


TL;DR:
No video after switching cases, boot seems fine. Computer will turn on once for a second or so, then reboot itself. Nothing changed software, hardware-wise.
Thank you very much.

 

[mcnumpty23]

while you have the motherboard out check the 4 pushpins have came through properly

common problem with the stock coolers is they dont engage properly--especially if you installed the cooler with

the motherboard in the case

the front panel connectors shouldnt cause no video signal if you get them wrong--but you can disconnect them

all except the power one to double check

 

[plzpuddngplz]

My bad. I forgot to say that I had only figured the power front panel connector so far.

 

[mcnumpty23]

how much thermal paste did you apply?

though too much or too little shouldnt stop it from showing video really

definately check those push pins though

 

[plzpuddngplz]

I didn't apply much thermal paste, only about half of a pea.
I'll get on the push pins.

Edit:
After double-checking the push pins and taking out the motherboard to check for shorts, the situation remains the same. Due to the strange behaviour of the first boot (turning on, restarting), I'm going to start by swapping out the PSU.

 

[plzpuddngplz]

All right, I'm now pretty sure something happened to the motherboard while I was transplanting it, and will try to get my hands on another to make sure that's the case. If anyone has other ideas, I'm still open to those.