+1 on fiddling with the garage door.
Most likely, there is a spring lock that the door activates by pushing the bar up when the door is pushed into the guides. I had a Monty Ward's box that did something similar. Even though the door was pushed all the way in, something was "just off enough" that the locking bars wouldn't release the drawers. I had to reach in and push/pull/bang/and swear to get it working again.
Another option might be to turn the box upside down and let gravity drop the bars. However, I wouldn't recommend this with your tools still inside. It could cause other problems when the tools shift.