I dropped a YN460ii and its 602 trigger down a flight of stairs in my house a while ago. It was a choice between the flash or the Jack&coke...I stand by my decision The flash no longer worked but the trigger was fine. I was sad but kept in perspective that it was only $45.
So when putting batteries into a new 460ii, I noticed that the batteries stuck out enough that I had to push the door in while sliding it to lock shut. Out of curiosity, I took the batteries out and looked inside to compare with the inoperative flash. I found that the flash that had fallen looked like the contacts at the bottom where mushed down, so the batteries would not offer resistance when closing the door. I used an allen wrench to pull the contacts up, then put batteries in. The flash powered up and worked fine! I threw on a trigger and test fired a few. Worked fine still!
So to anyone who drops one of these puppies and it doesn't seem to have any external damage but won't power up, hopefully this will be the only problem and easily fixed