I don't know why... but I found a solution!
I hovered my mouse over the icon on the Windows bar and instead of left-clicking as usual to open it up (which wasn't working), I right-clicked and then clicked "Maximize". For some reason this has worked when the usual method didn't! Hopefully this may help someone else in future.
I'm having the same problem with Windows 10. Haven't tried maximizing yet thanks for posting.
I tried hovering, but nothing happens, and when I right click, it doesn't give me an option to max or minimize?? I'm using Windows 10 - just got for Christmas, worked fine for a week, then today won't open. Have uninstalled 4 times, deleted all applicable files, etc.
Does anyone know of any other program to use with Overdrive in order to transfer to a Nook Color to read? I feel like they have no competition and I can't get any answers from anyone with Adobe