geforce graphics card problem with my pc :(

[trouble in graphics]

ok hi
basically my pc is acting like a dingus
i needed a new graphics card coz my onboard one just does not have the power to support anythig new.
so i go and buy a ge force 8400 gs
go to bios and change it from onboard to pci e
save and exit
go onto device manager and disable display driver
turn off pc
install graphics card
turn on pc
blank screen
see my problem
please help me before i throw out my
compac q sr5601 desktop please

[Allan]

Why did you disable anything in device manager?

Boot to safe mode and install the driver for the card and reboot. Let us know what happens.

[JJ 3000]

turn on pc
blank screen

Do you not get an image at all? Can you see the compaq logo when the computer turns on? If not, I'd say the video card is bad. Take it back.

[Quantos]

Did you connect your display to the new card? 
If you leave the display connected to the integrated video card it will do what you described.