Monitor doesnt show anything

Hello,

I had to build a new computer, the problem is that the memory ram was not good soo i wasnt able to install windows soo i ve set the memory ram to the lowest Mhz hoping that i wont get any errors while installing windows, but it still didnt work, soo i ve bought a new 1GB memory ram and remplaced the one that was not working, but now the monitor doesnt show anything no more, thats because i ve changed the Mhz of the memory ram in the BIOS and i cant reset the BIOS settings i ve already tried to do the pin trick to reset, but it doesnt work i ve also removed the CMOS battery (10 times!) and waited 10 mins then i put it back.
I ve also removed the processor and put it back, i tried everything even removing the battery while computer was running. I ve also tried to press the turn on button 30 sec while the power supply was off and then turning on the computer. I ve also tried to change the graphic card slot (i ve got 2) still didnt help. I ve also tried to put the old ram back and reset the CMOS battery but it didnt work, still nothing on the screen.
I cannot change the Mhz of the ram since i cant see anything on the screen.

The graphic card is a new one and it works on the other computers, the RAM is new too
The monitor is not the problem i have the same thing when i try with the other ones

The motherboard is ASUS M2N4-SLI
The processor is AMD Sempron (Thats what is written on it)
The graphic card is GeForce 8400GS 512mb
The Ram is DDR2 1GB (new one)

Plz help i ve tried EVERYTHING!!!!!