Hi DMW0805,
Welcome to the Apple Support Communities!
In your situation I would recommend using the attached article for troubleshooting. For best results, read over the information and make sure you are performing the connecting / disconnecting steps as recommended.
Mac notebooks: How to use your computer in closed clamshell (display closed) mode with an external display
http://support.apple.com/kb/HT3131
If you are using a wired keyboard and mouse:
- Make sure the computer is plugged in to an outlet using the AC power adapter.
- Connect a USB keyboard and mouse to your computer.
- With the computer turned on connect the Mac notebook (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
- After your computer's Desktop appears on the external display, close the computer's lid.
- When you close the lid:
- In OS X Lion and later, the external display will change to a blue screen, then will show your desktop.
- In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard.
You should now be able to use your Mac notebook as you normally would, with a USB keyboard and mouse.
How to disconnect your Mac notebook from the display after use:
For best results it is recommend that you put your computer to sleep before disconnecting your display.
Have a great day,
Joe