Computer not picking up video signal

Hello there, this happens to be my first post on these forums and hopefully you guys will be some help! Here is my issue.

Yesterday i was playing around a bit with stuff in my bios (playing with ram timings and things of that sort), and I did something that my computer didnt like and now when I try to boot it, it isnt picking up any video signal. Nothing is fried, but I cant seem to get it going. I've tried everything from reseating my cpu and applying more thermal compound, moving ram around, taking out one of my video cards (i run crossfire) tried each video card by itself and resetting my cmos various times. I did however, get it to boot up once earlier today when I had it with just one video card, got back into the bios and reset all to default then when I rebooted, it loaded up windows normal and then when I shut off the power and put the cover back on my case and put it back under my desk it went back to doing the same thing. Ive had this issue before as well as a friend of mine, neither of us really recall how it ended up working, it just did. Im open to any and all suggestions.