OnGuard U-Lock key mechanism partially activated I have a mini U-lock from OnGuard.
The lock is not attached to the bike, so that's not a factor is this question.

I can see the locking mechanism jutting out partially into the key hole, which is preventing the key from being fully inserted into the key hole--it only can go about 1/2 in.  How can I get the mechanism to go back in to place so that my key may be fully inserted? Or is it time to finally break down and get a whole new lock?
You can rotate the key back and forth while you insert it, That should help realign the cylinders. This actually a common problem and doesn't mean that the lock is broken. 

Take it to your bike shop if you continue to have problems. They are experts at the jiggle-dance sometimes necessary to get the key in.