Won't Boot... I Think

Hi
I've recently finished building my new pc. When I turn on the power the motherboard light comes on and the fan spins but I get no signal to the monitor and I get a very short quiet beep from the system speaker (so quiet I'm not sure that I heard it). Also at the start the fan spins for a few seconds then stops and continues spinning which makes it sound like it is booting, so maybe its is the GPU?

As far as I can see everything is fully connected. Really worried.

System:
Mobo - Asus P5QC P45
CPU - Intel Core 2 Quad Q8400 2.66GHz
GPU - Asus GeForce GTS250 512MB GDDR3
RAM - G.Skill 4GB (2x2GB) DDR2 1066
Heatsink - Random Zalman one
PSU - Coolermaster 520W Real Power

Any ideas on what's going on would be hugely appreciated.

The READ before posting about boot problems! sticky at the top of the forum was created to troubleshoot your problem. You should go through every step in the checklist.

Reading it doesn't do you any good. You actually have to perform EVERY step in the checklist.

Your CPU is supported by your motherboard beginning with BIOS 2002 which was released on 03/16/2009.

http://usa.asus.com/product.aspx?P [...] templete=2

So you've ensured that the 8-pin CPU power connector, main 24-pin power connector, and 6-pin PCI-E power connector are all firmly plugged in? Did you try booting with each stick of RAM by itself in the first RAM slot? Did you try booting with no RAM installed at all? Did you perform the breadboarding step at the bottom of the checklist to rule out a short?