A vga card should at least work in basic mode without any driver support.
What is your video card? Is it the same?
What mobo do you each have?
Here is a theory:
Is it possible that his motherboard requires a psu connection for added power for the pci-e slots?
Your mobo could be powered correctly which is why both cards work in your mobo, and his could be underpowered so if his card required more power, it would fail in his board while yours worked.