Black Screen Inspiron 1520 Need help assist

Hello, you expose the problem, take the time to read before you answer, I try to be as clear as possible.
Subject: Laptop Dell Inspiron 1520 + graph + Additional Card: Nvidia Geforce 8600M GT 512 MB

I had gradually black screens or off, up to this final and the Problem of black screen, but I hear that Windows Vista starts up the music of the opening of the bone , without being able to have the image.

I opened the pc, and actually a large pile of dust thermal paste + hard as concrete that I replaced, but ditto.
I ordered another graphics card thinking it was from the CG, but almost identical results except that I was the first time in a split second "dell logo" startup and then nothing.
I disconnected the battery ditto, black screen impossible to see the bios.
The pc runs except that damn black screen and display on another screen not

By dint of searching on forums, I tried to connect to another screen, the screen is recognized at boot but no display either.

1 / Is the two CG defective?
2 / Is it possible that it comes from the inverter?
3 / Is it possible for the processor is released?
4 / Is it possible that the screen is released?
If you can help me thank you in advance, I'm willing to try something

 

i m buying 2 hand parts

 

I had similiar problem with the Dell 1520 turning on but no image, non of the blinking codes were listed on Dell website either. I came across a thread of someguy having the similiar problem and all he did was open up his laptop and replace his CMOS battery and it booted up. So for 6 dollars I went to walmart and got me new battery and why not try it, beep and sure enough my laptop came back to life.