First you want to try and reset the SMC and PRAM
The PRAM is done by shutting the computer dow and pressing command, option P and R atthe same time, after it restarts, let go of the buttons and it will reboot
To do the SMC reset, follow this(copied from apple's article on this)
Shut down the computer.
Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
Release all the keys and the power button at the same time.
Press the power button to turn on the computer.
Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.
If this does not work, take a can of compressed air and spray it under the keys that are bad, removal is suggested, but not needed
To remove the keys, use a long nail(or have your friend with long nails do it, whatever is easier) and remember EXACTLY how you removed the key, and as to replacement, use your nail and remove the scissor hinge from the key and put it in exactly how it came off with the key
If this does not work, you need a new unibody assembly for this, they do not sell the keyboard separate, nor can it be removed
here is the guide to do so, the part needed should be in it