Full screen mode not working

If I press the "F" key or if I go to the dropdown menu under view/screen mode/Full Screen Mode, it flashes the "Full Screen Mode" for a split second but immediately defaults back to the "Standard Screen Mode". If I hold down the "F" key it flashes back and forth between the standard and the Full screen mode with tools, but as soon as I let go it defauts again to the "Standard screen mode". It's driving me crazy as switching between backgrounds is a huge part of my workflow.

I've updated the software to the most current. I've checked all the shortcuts and preferences and I can't find anything that's causing it to default to the standard screen mode only. Any advice? 

thanks,

-d