Hello! I'm running Niresh Mavericks. The system has been running great for the past year, but two days ago I was playing a game and then the display suddenly stopped (literally shut down). I rebooted the computer, and it booted with 800 x 600 resolution. I can only change it to 1280x1024 at most. I'm running Radeon HD 5850. I have NO idea what could cause this issue,can you help me please?