Thanks for posting this!! I was having the exact same problem. I have been searching and trying many things. Of course the dealer said I could come in... I knew how that was going to go. I did exactly as you said it all works! I have a 2 hour commute each day so you can imagine how much I needed the radio! Thank you saving so much money!I know this post is old but I can share my solution to this frustrating situation of the map DVD clicking when inserting and nothing loading.
SUMMARY SOLUTION - what I did was to use a can of compressed air to fix and hold upside down. Use at your own discretion and risk.
Even though this is an old post I am going to add my experience. I have a 2010 Highlander Limited with Navigation. It uses the maps disc from Toyota. Apparently over time and not necessarily a long time, there is a nylon gear in the unit which will not allow the disc to start spinning properly to load once the disc is ejected and put back in. The disc is needed running in the slot for the navigation to work. If the disc is missing or not able to be loaded properly then the navigation will not work. The proper loading of the disc apparently is part of the anti-theft system as well. If the navigation doesn't work but your radio and back-up camera works then the radio has not entered the anti-theft mode which happens when there is no longer power to the radio/nav unit. You know that happens when the entire head unit is not working at all - no radio, no back up camera, and can't get into any control, or menu screens. All you can do (in my case) is open/close the screen to access the navigation DVD slot. Like this OP says, he ejected the Navi DVD and now when he puts it back in, the unit grabs the DVD like it should but when it goes into the slot and should be loading all he can hear is a clicking noise like it is trying to load - read back about the nylon gear which has stripped at least a tooth or two. Mine was doing this.
So, in my case, I searched online and read that some have fixed this problem by 'thumping - tapping - slapping - beating' on the deck while the disc is clicking. This probably is best done by removing the trim and 4 bolts holding the unit in place then, without removing any wires (remember about removing power will trigger the anti-theft feature), hit, thump, tap, etc the unit while it is clicking. This may allow the unit to have that stripped gear grab the next tooth and begin to load properly. I did this with no luck while others had luck.
So, somewhere online i read where someone had some luck with compressed air in a can so i gave that a try. I had a can already in the garage so I started with that. It was your regular can of compressed air and had a 5-6 inch red tube. Holding the can upright as the DVD was clicking I inserted the red tube and blasted the air full trigger in the DVD slit back and forth. Did this several times all while the DVD was clicking away with no luck. The can was not full so only after 5-6 tries it ran out. Keep in mind that because the red tube was so long that I was able to keep the can upright which only blows air from the top and not the liquid propellant that is at the bottom of the can.
Since my air ran out I went to Walmart to get another can. The ones there only come with a about an inch and a half tube but I bought it anyway knowing I had a longer tube at home. This is relevant because the longer tube allows it to be inserted in the DVD opening while the screen is horizontal and the can stays upright but while using the short tube you have to hold the compressed air can upside down which means the liquid propellant will come out of the tube. While the compressed air is dry and warm while using the long tube and holding the can upright, what comes out with the can upside down is wet and very very cold and has substance. Since my long red tube at home wouldn't fit the new can I said what the hec and blasted away with the can upside down, while the DVD was clicking, going back and forth just like before, except this time the DVD quit clicking and the DVD sounded like it was loading.
It didn't load but the clicking stopped. The screen finally closed on its own but didn't load information. The screen stayed the same. I figured that the extreme cold easily could have literally frozen something and needed a few minutes to 'thaw' out. After about 2 minutes, with much trepidation, I pressed the open/close button on the frame and the screen opened and the DVD ejected. The DVD was still very very cold to the touch and has frost on it. I wiped off the frost and gave the DVD about a minute or so to get to the outside temp. During this time, the deck itself I'm sure began to 'thaw' out also.
I inserted the now warmed back up DVD and no clicking. The screen door closed and DVD started loading and the screen showed the loading progress. Once it was loaded and the deck reset itself, the Toyota logo came up and the navigation showed the map of my house/street, the radio worked, the back camera worked, and all functions were restored.