I have an article for you that can help you troubleshoot this issue and can help you rule out some possibilities. The article can be found right here:
The specific part of the article you will want to turn your attention to can be found here:
No video or no signal, image distortion, "snow," or flickering
When using an external display be sure to check the following:
- If you're using an Apple notebook, confirm the AC power cable or adapter is securely connected to the computer and the cable providing power to the display is also secure. It is always good to have your notebook connected to AC power when an external display is in use.
- Confirm display adapters are fully seated in their respective connections and that they are supported models and for the computer and display. Refer to these articles to assist you with adapter compatibility and further configuration information:
- Remove all display cable extenders, KVM switches, or other like devices and retest to determine if the issue is resolved.
- Try unplugging the video adapter or cable and then plug it back in.
- If more than one video adapter is in use (or "daisy-chained"), troubleshoot by using only one adapter.
- Example: A mini DisplayPort to DVI adapter connected to a DVI to HDMI adapter is an unsupported configuration because there is a series of adapters in use.
- If available, try using a different display and or adapter (or use a different connector by using DVI instead of VGA, for instance).
Reset the system
You can reset the Mac's parameter RAM and SMC.Reset the resolutionStart by resetting the Mac's parameter RAM. If the display does not come up, was previously set to an unsupported resolution, and still results in no video:
- Start up in Safe Mode.
- From the Apple () menu, choose System Preferences.
- Choose Displays from the View menu to open the preferences pane.
- Select any resolution and refresh rate that your display supports.
- Restart your computer.
Thanks for coming to the Apple Support Communities!
The odds are that you are correct. If the MBP appears tp be operating normally but the display is dark and an attached monitor display is also dark, the the GPU is the prime suspect. Make an appointment at an Apple store genius bar and have it definitively diagnosed. It is not a inexpensive repair. The entire logic board will have to be replaced if the GPU has failed.
Thanks Braden85 and Ogelthope for your input. I tried a couple different things, and ended up bringing it into the Apple store to get diagnosed. They agreed it was the GPU, and the logic board needed replacing.
Just in case anybody else was wondering, I just had them send my computer to the warehouse in TN, and for $280 they replaced the logic board, the trackpad (non-responsive click), and the whole display (looked pretty used with the apple logo "burnt" into it). I dunno if this was the most cost efficient approach, but with a new logic board it runs just as fast as it did when it was working properly.
This approach gave me a 90-day AppleCare service for any issues with the new parts. Hope this helps anybody with similar issues!