I recently built a gaming rig with two Radeon HD 5770s (manufactured by Diamond) hooked up. I ran GPU-Z to see how stressed they were when playing certain games. But when I ran it, I noticed it didn't recognize my second graphics card. I checked device manager and it also didn't recognize the other graphics card.
I opened up my computer and made sure the pci-e power connectors were connected properly and that the card was seated properly. Those both checked out. I then tried reinstalling the drivers which also did nothing.
Here's the thing though, when i first built my computer (Beginning of August), crossfire worked perfectly and GPU-Z, Device Manager and the Catalyst Control Center both recognized the graphics cards.
I'm not too much of a computer whiz so i'm hoping it's just something I overlooked in the BIOS or something small like that.
Windows 7 Ultimate x64
Radeon HD 5770 x2
AMD Phenom II x4 965
4GB GSkill Ripjaw DDR3
Asus M4A88TD-V Series Motherboard
Intel 40GB SSD
Hitachi 1TB and 2TB Deskstar HDDS
Corsasir 750W Power Supply