My monitor won't pick up a signal!

Hello,
Recently I've been running into problems with my computer freezing, so I browsed a few forums and someone suggested that one of my video cards could be causing this. I disabled one of the cards (the one that i was currently plugged into which caused me to plug my monitor into the other card, but that worked fine) and screwed around until my computer froze. I turned my computer back on a few minutes later to switch the cards around but i could never get a signal on the screen back. I switched the cable around numerous times, but was never able to get a signal. What do I do???