I'm having some issues with crossfire under windows 8.1.
Basically one of the 7970 chips on the 7990 is showing as being disabled and the crossfire option is missing from CCC on an intermittent basis. Sometimes I can enable it, but more often than not the option is not avaiable.
I have tried reinstalling drivers, uninstalling, cleaning (driver cleaner and amd cleaner) and the problem persists. I have tried a number of different drivers, the last 3-4 issues, without change.
Power is not an issue (750W supply), nor is heat.
Anyone have any suggestions about how to fix the issue?