New build won´t boot

Yesterday I did my first build with this hardware:

Asus P5N32-E SLI
Core2Duo E6850
Thermaltake Toughpower 750w
2x2GB DDR2 800 OCZ Reaper-HPC
8800GT

I've connected everything. The green led on the MoBo lights up. I press the power on button and psu, cpu, gpu fans begin to work, even I can hear the hardisk running, but the computer won´t boot. I don´t get any beeps nor video signal.

I tried to disconnect everything and power on with CPU+Video+RAM only, getting the same results. After that I've reconnected everything outside the case with no success. I double checked cables from the PSU to Motherboard and Videocard. I also checked the MoBo for damage but can´t find any broken/burnt components.

Since I've unplugged everything to reconnect it outside the box, I removed the heatsink from the mobo to check if it was well seated. It seemed so. My question is: could that be the cause of my no-boot problem? is it necessary to put some more heat paste between the cpu and the heatsink if I remove the heatsink from the MoBo? Or the original heat paste already on the CPU/heatsink is enough?

I don´t have any other MoBo, CPU, Videocard or RAM so I can´t test these devices separately.

Do you have any suggestions? Thanks in advance

 

I have read on other forums that mobos usually have jumpers which need to be configured first. Sorry if this is pants info as I am a noob and you may have put me off my first build. Haha.

 

I've checked these things. I replaced the thermal paste too. No luck