Generally, the keypad does not need to be changed. Usually, one of the flex connectors in the flip (screen/camera) portion of the phone is loose, dirty and/or corroded (maybe from water, sweat, wear, trauma, etc). This is relatively easily fixed by a semi tech savy consumer. You will need a size T5 star driver (and possibly a T6) and a small screw driver, along with some rubbing (isopropyl) alcohol and some Q-tips.
For more information on servicing your phone, you should do an internte search for RAZR dissassembly http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=GGLJ,GGLJ:2006 -45,GGLJ:en&q=razr+v3+disassembly
and you'll get lots of hits including videos like this: http://video.google.com/videoplay?docid=-5120755491924318860
When you have the top case dissassembled, the connector with the black patch on the top is likely loose. Clean the connections thoroughly with alcohol and a Q-Tip and reassemble. If it doesn't work, or only works partially, another cleaning may help (I had to go in twice).