Macbook Pro TrackPad not clicking
This video recommends resetting the SMC:


Turn off your computer.
Plug in the MagSafe adapter.
Press Shift-Option-Control, on the left side of the keyboard, and the power button, at the same time and hold it for 5 seconds.
Let go of all the buttons.
Turn your computer back on with the power button.


For more information on the SMC reset see this Apple support article