I found a great article about troubleshooting an external display with your Macbook Pro called Apple computers: Troubleshooting issues with video on internal or external displays found here http://support.apple.com/kb/ht1573.
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.
- 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.
Using Closed Clamshell, Extended Desktop, or Mirroring display modes When using multiple displays, information can be presented in a number of ways. For more information and what modes are supported by your Apple product refer to:
should have been moved to the macbook pro forum for on
This forum deals with a desktop/tower 65lb Mac Pro
Direct you to the proper forum for MacBook :