My passenger side door lock wont lock at all. Not by the lock button or manually locking. Its very stiff when I try to lock it manually, and when it does move it goes right back into unlocked position. I dont know much about locks or even this car just bought it a few days ago. But I want to get it fixed before I start modding it. Last thing I need is it get stolen, and I live in the city. Please help, its 99 Grand Prix 4 door GTP if that matters.