need compatible motherboard

i'm building a computer and i got all the parts together, but when i tried to run it there was no video, at first i thought the video card was broken but it turns out that the motherboard wasn't compatible with the video for absolutely no reason. in order to get it to work i had to but this beta bios on it but if i did that then it would void the warranty, so i ended up sending it back. so now i need to know if anybody has any idea of what type of motherboard i could get in order to get this stupid thing to work.

i have a quad core 3.0Ghz 1333mhz processor, Radeon 4870x2 video card (eventually i want to get a second one so i need a crossfire supported motherboard), and 4x2gb 800mhz ddr2 RAM.

i ordered an x38 motherboard but didn't find out that it wasn't compatible when i put it together, which was a huge pain in the arse for me. i've been trying to find out all over forums for people looking for the same answer but every single time i find a forum with somebody asking this question people always just give these extremely abstract answers.
like, "you shouldn't worry about the motherboard, make sure the PSU is compatible" or "you should bother with it because nobody in the world needs that much power in their computer" and stuff like that. so yeah, no BS answers please, just some help on what motherboard is best for my current position, thanks.