Power locks wont lock

[ctd2001]

I have a 1990 4runner and the power locks will not lock down. When you hit the lock button, you can hear them trying to lock but they wont go down. You can not even lock them by hand or with the key. It seems as though they are jammed, or at least one of them is. None of the locks will lock, even the back doors. The only look that works is the one on the tailgate. What could the problem be, thanks for your help