My key won't work in my dead bolt door lock. I can turn the lock from the inside fine and also when the door is open. But I can't use my key to lock the door. Any suggestions?

Bad key? It could be the mechanism inside. There is a part of the mechanism that is only for the key. It has nothing to do with the inside latch. It could be something inside is worn out or the tumblers that hold the key signature are worn or upset somehow. This is one of those things that requires experience. I would take it off the door and bring it to a locksmith. You can get one to your house if you can't leave the door without the deadbolt, but it'll cost you to get him there. It may be easier to replace it. Deadbolts are not very expensive these days and are fairly easy to install.