I purchased Popcorn 3, loaded it on my Mac, installed appropriately, and nothing. It doesn't even start. I put it in my doc and thought, maybe it has to have a home

-- nope, still doesn't work.
Installed it 3 times. Still doesn't work. Thought, okay, even though I've loaded many, MANY programs on my Mac, maybe this one doesn't work because it hates my Mac, so I took it over to my son's and loaded it on his Mac. Doesn't work.
So it's not the computer, or his computer, it's the software.
I can't return it to the Apple Store (tried) because they say it's been opened. Well YEAH have to try it! And if it doesn't work? too bad. You're out $50.
Any suggestions how I can get this thing to work?
Be thankful you are even HAVING problems with your Popcorn -- that means it at least IS working!

I have nothing!

YEP!!!
I feel your pain and frustration!!!
I have been having the same issue with this poorly made software.
They don't even support it anymore (or so it seems)!
I have moved on to better software!!!
I use VisualHub. It costs less than half of popcorn and does more.
The developer will respond (personally ) to all e-mails......
If you have an elgato .264 you might want to look into Roadmovie.....
Good luck on getting your money back (EBay)
The sooner you walk away from this crap the better you will feel!!!!