We have encountered a strange problem with our DirectX 9 application when it's running on Windows 8.1 x64. The application is working correctly in windowed mode, but when we go to fullscreen mode the GPU stops working completely (according to GPU-Z). It only renders the first image and then nothing. The application is still running - you can hear sounds and click on GUI items, but the image on the screen is completely frozen. The only thing that seems to help is to alt-tab out of the application and then back in. After that the GPU seems to wake up to render images again. Going to windowed mode and back to fullscreen mode freezes the image again. Alt-tabbing to the desktop and then back to the application is the only thing that seems to work.
Any ideas what could be causing this kind of thing? We have only encountered this problem on Windows 8.