I'm sorry to hear that you are having trouble with Juicebox-Pro.
Here are some notes which might help.
First of all, for anyone else reading this thread and experiencing difficulties getting past the loading screen , please read this forum thread and be sure to install the latest version of AIR with WebKit support which, at the time of writing, is AIR v184.108.40.2063 (go to Harman's AIR download page and scroll down to the foot of the page).
It sounds like you may have found it already but I've written a fairly comprehensive post about unresponsive 'Open Gallery' and 'New Gallery' buttons here. I've really not left anything out and anything and everything that might help is documented there.
A .tempGallery folder will be created only after the 'New Gallery' button has been clicked or when an existing gallery has been opened (and should automatically be deleted on closing the application). If you cannot click either of the 'New Gallery' or 'Open Gallery' buttons, then you won't have a .tempGallery folder so this, in itself, is not unexpected.
There is no AppData\Roaming\Adobe\AIR\ELS\JuiceboxBuilder-Pro
The ELS/JuiceboxBuilder-Pro folder should be created as soon as JuiceboxBuilder-Pro is first run (and there should be several Private Encrypted Data files inside the folder).
If you don't have this folder on your system, then this could certainly be the cause of your problem. Something may be preventing the ELS/JuiceboxBuilder-Pro folder from being created (or preventing AIR from writing the required files to the folder).
Make sure that you install both AIR and JuiceboxBuilder-Pro under an Administrator user account.
Also, when installing AIR, try right-clicking the 'AdobeAIR.exe' installation file and selecting 'Run as administrator'. (You can do this for AIR but not for JuiceboxBuilder-Pro itself so don't worry that the 'Run as administrator' option is not there for JuiceboxBuilder-Pro.)
I still get an upgrade to Pro message even though it says it is Pro.
That is most definitely a problem and one that shouldn't really be possible.
JuiceboxBuilder-Lite and JuiceboxBuilder-Pro are two completely separate applications that can be installed and run side-by-side on the same computer without interfering with each other. They are installed into different folders and their files should not mix. There really ought to be no way that JuiceboxBuilder-Pro should be able to include a link to 'Upgrade to Juicebox-Pro!' at all.
Over the years, I've heard of this only a couple of times before and the cause both times seems to have been a corrupt user profile.
Can you try creating a new Administrator user account on your PC and installing AIR v220.127.116.113 and JuiceboxBuilder-Pro v18.104.22.168 under this new account? This should hopefully work fine.
I really don't know what might be at the root of the user profile problem but this should hopefully at least give you a useable workaround.
Maybe the other suggestions in the forum thread I mentioned above (here) will also help.
Please let me know how you get on.