Why are the doors not locking on my Yukon Denali?

I have a yukon denali 2008, i recently went to lock the doors and when i went to test them, they still opened, the alarm went off and all. The driver side door has been out for a while, and i wasn't aware of all the other doors were not locking either. i didn't know what to do, could this problem be fixed without bringing it in?