I have an Asus Q550-LF computer running Windows 8.1 Enterprise. It has a MiniDisplayPort output which is connected to a MiniDP to DVI adapter. I discovered that my monitor was not working the same day I turned off SecureBoot and turned on Legacy mode. On a whim, I re-enabled SecureBoot/disabled Legacy mode and my monitor magically works. It might be worth mentioning that the monitor isn't even DETECTED when SecureBoot is off/Legacy mode is on. It's shown nowhere in any driver config areas.
This leads to two questions:
- Why does this happen? (I am using latest drivers)
- How on earth would I fix this?
Update (8/17/14): Thinking about it, this problem seems to be caused more by CSM/Legacy Mode than Secure Boot. I have yet to test this idea though.
Update 2 (8/17/14): Testing the system shows that it is the fault of CSM/Legacy mode instead of Secure Boot. The system works fine when Secure Boot is off. It breaks when CSM/Legacy mode is on.