Computer wont start up with crossfire 4870's

[brianlt]

Hey so i just bought a second ATI HD 4870. threw it in my machine, put the bridges on, went and got the 4870 driver from ati's site and now when i restarted my computer it goes through the bios and then the little windows loading bar shows up and starts loading, then goes away and my screen goes black. and stays black. the monitor light is still on as if its reading from the computer. i can run in safe mode, and i can run when i take one card out. and either card can be in but when i cross fire them and THEN UPDATE THE DRIVERS when i restart is when the screen goes black. the two 4870's are different brands and dif memory sizes, thought that wouldnt make a difference cuz crossfire is flexible but maybe not. help =(

my components are Asus Rampage formula motherboard, Rosewill XTREME series 850 power supply, intel quad core 2.8, 8gb ram(forgot the company, 2 dif companys) 1 4870 512mb vision tek (bought about 2 years ago), and 1 4870 1gb XFX that i just bought

 

[mister g]

I'm sorry I know that Nvidia lets you do SLI with different company cards but I'm not sure about ATI. Anyway did you set up the mobo correctly? Otherwise go to the Asus website and flash for the latest BIOS. I heard that some mobos don't need the ribbon cable to do Crossfire.

 

[brianlt]

FIXED IT! thanks for the input though, i was reading some other forums and apparently it had to do with the power supply. it needs 4 of those 6 pinned ones and i didnt have enough so i had to get those adapters and apparently they were connected through some other things and they needed to be connected DIRECTLY from the power supply cords. so it finally worked