I'm trying to intall a video card and the monitor won't respond.?

I installed a new card and I got it running and the computer was working fine. The power supply quit working (would boot up and then shut down). I put a whole other power supply into it and now the computer will run but I can't the old card or the new card to respond. The monitor won't pick up the card and it just says no signal. There isn't any on board video so I can't tell what it's doing. It is an AGP card so there is only one slot on the mother board. Any ideas?