interesting...
In my case, I let it sit for a minute or two before powering it back on.
Today we had about 102 degrees in the afternoon, so I decided to make a little test: I parked my car on a parking lot under the burning sun with all windows rolled up and moon room cover opened (so that the car could get as hot as possible...) I kinda regret I did that when I got back into the car... But anyway, I let it sit like that for good 40-50 mins and when I got back - it would just sit at the Pioneer boot-up screen. I turned off my car, waited a few mins and turned it back on - same result.
Then I took a 10 min drive on a highway with all windows opened. When I arrived at my destination, I power cycled it and it worked.
I'm taking it back to the installer tomorrow. They probably hate me by now 
I just hope that they will give me a new unit and this will never happen again.
I would still have to blame the HDD for this. I would assume that it goes through the BIOS just fine and it just hangs loading the actual app from the HDD.
Let's take everybody's fav Windows for example. If you will mess with some system files and/or with registry, Windows just won't boot. It would sit at the boot screen with the scroll bar constantly moving, but computer wouldn't be doing anything. It is basically at a deadlock (where it cannot finish a certain action and other actions are waiting indefinitely until current action completes)
But so far, I am VERY disappointed in this product 
dimaj