macbook screen is dim and cannot change brightness

I just read, about someone with a similar problem.

Try holding the command key while pressing the brightness up or down button.

If that does not work then i would suggest resetting the PRAM (which stores system settings)

However before you do so make sure you understand what you are going to loose, so read up about it here first:
http://support.apple.com/kb/HT1379?viewlocale=en_US

-Resetting PRAM and NVRAM-

1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

Have you tried restarting the MacBook since you removed the peripheral device?