"Why does my door bounce off the strike plate when I try to shut the door?"

The latch is dry and needs a shot of WD-40.  If this does not work, the latch is broken.  You can go to your local hardware store and buy the proper latch.  Ask the salesperson to show you how to do this.  Before going, however, be sure to read the name of the lock from the face of the latch itself.  It may say Schlage, Kwikset, Callin, EZ Set, or Baldwin.