PC does not start with Nvidia GeForce 8800 GTS

Hello,
I wanted to change the graphics card after noon, moving from a 8600GT to a 8800 GTS.
Unfortunately, I could not handle the miodification because once the graphics card placed on the motherboard, I could not access my SATA connectors motherboard.
In short, no matter, I have withdrawn my 8800 and handed over my 8600, and that is that the problem arises: PC seems to start, but the screen remains in standby mode and nothing is displayed.
The problem is always the same if I try to connect my screen on the form of integrated graphics chipset on my motherboard.
The only solution open to me at the moment is to remove the graphics card and use my screen on the graphics chipset on the motherboard.
Have you any idea what happened?

thank you in advance!
Good day

Hi trying on a clear cmos .... may be this could help.

Thank you for having responded to my post, I inquired about the clear cmos, but is it really possible that without rebooting the PC, just by changing the graphics card and giving the former, the bios could be amended ?
If so I'll try this solution.

Thank you in advance!

To make a clear cmos, you remove the battery for 15 minutes

I do not know but there is no good reason for its fair, many people have already made a clear cmos and I know u are never a problem!
otherwise I do not see too much or may be the problem

A big thank you especially to you for your help, I remove the battery, 15 minutes later I presented my card, then the battery, I booted, and the magical, my screen was lit: D
Thank you a lot for your help!