1996 Acura Integra power door lock

I have a 96 Acura Integra GS-R Hatchback, the drivers side door lock cannot be manually locked from the inside and will not lock when I hit the auto lock button, but the passenger side works perfectly. The only way to lock the driver's side is manually from the outside. What do you think the problem is, where could I get the part that needs to be replaced, and how hard would it be to replace myself?