Running a gigabyte AMD R9 380 card and getting similar problems.

the system boots, loads the driver and the fans briefly spin to 100% before the
video goes completely dark and the monitor turns off.  the card is detected as
a Tonga PRO 285/380.  

this issue is going to become much more critical in the next week, as SteamOS
just switched their AMD proprietary drivers for amdgpu open source drivers.