I recently bought a second XFX 5770 1GB to crossfire with my other card (also a XFX 5770) after plugging everything in and attaching the crossfire bridge, the crossfireX tab in CCC never showed up. I had this happen to me before with two 4670's a year a ago when i upgraded to Windows 7 64 bit. So i did what I did with the 4670's and went back to vista 64 bit. However with the 5770's this didn't work so i have cleaned out all the old drivers and installed the latest ones but nothing. I can't enable crossfire. The second 5770 is showing up in the CCC device manager so the PCI-e slot is working fine.
I have a Dell Xps 630i with a Nvidia 650i SLI motherboard.
When you cleaned out the old drivers, did you do this with a utility? Or just "Uninstall" them? Use something like Driver Sweeper to remove them completely (going into Safe Mode, etc).
Is it possible any BIOS settings have been changed since? Or any BIOS update/flashing? Cause that usually sets things to default, and you might want to check settings there.
Other than that, you can try different versions of the ATI drivers to see if another older/newer version works.
Yep I actually used Driver Sweeper I have reset the BIOS to its defaults after overclocking the CPU a few weeks ago. I also tried different versions of the ATI drivers and the drivers that came with the cards.