It’s a really simple problem that is being caused by pop up window you can’t see. To access this pop up window, you need to  right click along the top of the frozen window and you should see a small menu that gives you the option the Maximize the window. Click on Maximize and you should then see the pop up window that was previously hidden. Once you see that window, close it and then you can access the frozen window and then get into Proseries.