I also find that completely closing down Plarium Play fixes the issue too, which likely does the same thing that Skadi is saying. When I say completely close down Plarium Play, I mean right-click on the icon in the lower right corner and choose "Exit" or "Close". Not just press the X up the top right corner
When you run it again then it should actually take about 5 to 10 seconds to open, and there will be a brief Plarium Play loading screen. If it opens up straight away then it wasn't closed down completely