System doesn't boot: no beeps

I've just upgraded my Athlon 64 X2 4200, DFI Lanparty Ultra-D system with 2GB to an ASUS A8N32-SLI Deluxe and a Thermaltake big typhoon.

I did everything correctly as far as I know, but now the system doesn't boot at all. I mean, fans work, everything kinda lights up as expected, HDD spins up, and all, but nothing happens. No beep or anything. No monitor output either.

I've checked the clear CMOS jumper, but it's in the right position. I've tried reversing the reset switch; I've even tried using nothing but the power switch (I read it somewhere that this could be a cause for problems).

Now the only thing that occurs to me is that I may have put a little too much thermal paste, but I used nonconductive Arctic Silver Ceramique, which should therefore not be an issue in any case. When installing the big typhoon, I tightened the screws quite a bit, because the heatsing is heavy, but because any screwdriver has to be used kinda sideways when installing this cooler, I didn't really push the screw too much... I think. Could it be that I applied too much force to the big typhoon? But this is a lidded processor, with IHS...

What did I do wrong? I have no idea. Anyone has any idea?

Thanks for your help!

I've tried reseating my RAM and video card, but got nothing.

I got worried about the processor, and took off the big typhoon and CPU from the motherboard. It all seemed just fine, nothing wrong - at least not visibly.

I'm left with only a few alternatives... Either the new mobo isn't OK or I've forgotten something that is shortening the system. I have yet to clear the CMOS, though.

The motherboard was ordered online, as was CPU and memory, but they're all under warranty. So the only sad thing here is that I'll have no computer for now. I still have the old mobo, so I could test to see if the previous configuration (still) works fine, but there'd be no real point in doing that...

Ah damn, I probably just forgot something unplugged or whatever...

I've got an OCZ Powerstream 520W - which is most likely not the problem.

I'm actually switching from DFI to ASUS (to A8N32-SLI Deluxe)...

Still got nothing, but I've given myself a break so I don't go mad (or start crying all over the place because of this damned computer!)...

I've tried testing the RAM using another computer I have at home. It's an Athlon XP 2600 that confirmed that there's actually nothing wrong with the memory.

I'm beginning to think that I got a faulty mobo....