I skimmed through the manual for the DVD-CV35, and didn't see any reference to a key lock. You can try to reinitialize the player by stopping the player, hold down the track reverse and pause keys, then press and hold the open/close button for about 3-5 seconds.
You may want to dig through the manual a bit more than I did. It is available from Panasonics website. You'll find it here: http://service.us.panasonic.com/OPERMANPDF/DVDCV40.PDF
(It's the same manual for the CV40 and CV35)