Actually I am having the same problem again and can't figure out exactly how I got it to work before. Windows key plus arrows did not work. I somehow stumbled across getting it to work before by using the TASK VIEW button on the task bar.
Here's a more permanent fix: if you have an icon for Evernote on your desktop, right click, and go to PROPERTIES, click on the SHORT CUT tab, and make sure the RUN field shows MAXIMIZED. This solved the problem for me without having to maneuver the window every time I opened it.