Short version: Why would a WQHD monitor that worked under 13.3 and 13.4 disappear under beta 13.8, and still be missing after reinstalling 13.4, but be visible to the system before the driver starts operation (BIOS and start of windows boot) or with the driver completely uninstalled?
ASRock Extreme4/Gen3 w/ i5-2500K
on-board video driving a Sharp TV at 1080p
HIS 7870 ICEQ driving a WXGA+ Dell (DVI) and WQHD HKC T7000 (HDMI) as my primary
System has been working perfectly for over 6 months, first with 13.3 and Windows 7 and then 13.4 and Windows 8, with the HKC monitor being driven at 2560x1440@60Hz. The HKC monitor fully supports HDMI 1.4 and Displayport 1.2.
I decided to upgrade to beta 13.8 and when the driver installed my HKC monitor disappeared. The Dell and Sharp continued working, but the HKC showed no video input. Checking Device Manager, the HKC monitor was no longer visible to Windows.
Rebooting my computer, the HKC worked fine through BIOS and the start of Windows, but before getting to the Windows 8 lock screen, the monitor stops being driven and the Sharp becomes my primary.
Removing the driver and rolling back to 13.4 did not help, the HKC monitor still disappears as soon as the Catalyst software loads the video driver. Uninstalling the video driver allows the HKC monitor to be seen by Windows as plugged into the 7870 HDMI port- both the HKC and Sharp show up as Generic PnP monitors, though the Dell is still seen as a E198WFP(Digital).
I thought for sure this was the HDMI port being disabled and I just needed to find a bit to flip in a config somewhere, but as a test, under both 13.4 and 13.8, plugging the Sharp into the 7870 HDMI port works fine, even while the HKC is plugged into the on-board video (though the i5-2500K apparently can't drive beyond 1920x1080), thus the HDMI port isn't being disabled, it is just refusing to acknowledge the existance of my HKC.
As a test, I plan to get a DisplayPort cable and see if that works. Any other suggestions would be greatly appreciated, though. I have never tested this monitor for whether or not it could be overclocked beyond 60Hz and would like to test that ability with beta 13.8.