Ha true, you should still get some sort of display from the onboard graphics card. I've had a Google and some people who have had the same issue and found it could be that the motherboard is broken or isn't compatible with graphics card. It could also be that the card slot is not functioning correctly.
Try taking the new graphics card out and just using the onboard card to see if you get a display or you could use try inserting the card into a different mothorboard and vice-versa to see if it's a compatability issue or if one of them isn't working.
Do isolated tests on each component. Use your motherboard and everything else from your friends computer to check it isn't the motherboard, if your motherboard has more than 1 G-card slot swop the card to check it's not just the slot. check your monitor with your friends macheine too, sounds obvious but easily over-looked.