15" core i7 displaylink woes

[doctorkrit]

I have Macbook Pro 15" i7 and had the same problem, which I figured out that it was because of the system's confusion about primary monitor. As this problem does not happen to my Mac Mini at all, I hypothesized that it is because the Macbook's own monitor was failed to be recognized.

In my case, I installed the DisplayLink (DL) driver when my Macbook Pro was connected to Apple Cinema Display 24" (ACD) in close-lid mode. The system then remembered the ACD as primary monitor and the USB monitor as secondary. When I disconnected my Macbook Pro from the ACD, the system therefore could not find that primary monitor anymore.

After many trials and errors, here are the long steps I did successfully:
- Shut down the Macbook. If you can't see anything on the screen, just press & hold the power button for 10 seconds
- Connect the Macbook to non-USB external monitor (VGA, DVI, Mini Displayport, etc.)
- Turn on your Macbook. You should be able to see both external and Macbook monitors.
- Go to System Preferences > Displays to make sure that your Macbook's screen is the primary monitor (with menu bar and dock) and the external one is secondary monitor
- Unplug the external monitor. The Macbook's screen should blink once and become the one and only monitor
- Uninstall the DL driver. The Macbook will then restart. You should be able to see your Macbook screen afterward
- Try connect with non-USB external monitor again to make sure that your Macbook's screen is still primary monitor. If not, go to System Preferences > Displays to make it primary.
- Install DL driver. The Macbook will then restart.
- Connect the USB monitor and make sure that your Macbook's screen is still primary monitor. If not, go to System Preferences > Displays to make it primary.
- Connect non-USB monitor. You will now have 3 monitors. Make sure that your Macbook's screen is still primary monitor. If not, go to System Preferences > Displays to make it primary.
- Disconnect both USB & non-USB monitors, your Macbook screen should be working fine.