You may need to define which Nvidia video card is used every time you launch Plays.tv.
Follow these steps to set that up:
1. Open NVIDIA Control Panel
2. Select "Manage 3D Settings" on the left, under "3D Settings"
3. Navigate to the "Program Settings" Tab.
4. Find or Add the Plays.tv Client to the Application List.
5. The following setting should then be switched for playstv.exe.