PC fails to find graphics card on boot up.

vdu?

what are your sys specs?

Pardon me for being condescending, but I'm assuming you have installed the drivers, right?

Run it with the Onboard Graphics Card, boot into BIOS. Choose the right Display Order,
PCIe-PCI-Onboard or PCI-PCIe-Onboard.
Save and exit. Shutdown system
Reconnect the VGA cable to the GPU in your PCI/PCIe Slot.
Start up the system.
See if this helps.

Check to make sure the graphic card matches the board
Check to see if you need your bios upgraded
Set bios like alyoshka said for the right display order.
Also might need to use on-board graphics card until you install the drivers for the graphics card and make sure you get the lastest from the maker of the graphics card

hope one of those steps help you out

Also make sure the power cable is connected to the card as well, if it requires one.