New 256 MB Video Card Shows Black Screen

Disable onboard video in the bios before installing the new card

Bios my be entered by pressing DEL, F1, F2 Or F10 keys at booting.

Turn off PC

Insert card on motherboard PCI or AGP slot

Connect monitor to video card

Turn on PC 

Start Windows in Safe Mode...Press and release F8 key

Disable Onboard video in device manager

Restart Wndows normally