2000 4runner door lock does not lock

My 2000 4Runner door lock stops working today.  I tried locking with the remote but it does not lock.  Only unlocking worked.  I also tried to lock the doors manually by pressing the door lock buttons inside the car.  That didn't work either and again, the unlocking buttons worked.  However, if I manually lock each of the door one by one (by pushing down on the locking pieces that are next to each window) and then pressed the lock button on the remote, it makes a beeping sound indicating that it is locking/the alarm is set.  Does anyone have any idea what is wrong and how to go about fixing it?

Thanks,

TD

Do you have an aftermarket alarm/keyless entry system installed?

If no, then it sounds like there's something wrong with your door lock relay system.  You can meter the BROWN / white wire (below the fusebox) to see if there is a voltage fluctuation w/ the doorlock button on driver's door or with the keyfob button.  If you can get ahold of a repair/service manual with the electrical wiring diagrams (EWD's) you can trace the unlock wire back to the door lock/unlock relay system and determine more specifically where the problem is. 

As a matter of routine, check all engine bay and interior fuses.  Sometimes dome light fuses are linked to the door lock relay system -- did your dome light go out recently? it's a 7.5A fuse.