I recently ran into an issue after remoting into a Windows machine using RDP where I saw a completely white screen. My initial response was to hit CTRL + ALT + DEL, but this pulls up the task manager on my local machine, not the remote machine with the white screen.
Here are a couple of Windows shortcuts worth trying:
CTRL + ALT + END
This will allow you to pull up the task manager in an RDP session if you are unable to right click on the start menu.
ALT + F4
This command will close the current active window. In my case, this worked to get rid of the white screen.
Full credit goes to Erik Ramsgaard Wognsen for bringing this to light.