First, check the following:
Check if your GPU meets the GameStream requirements. You can get this information under, Settings > General > Features.
Check if MSVC Runtime package version 12.0 or higher is installed for both 32-bit and 64-bit architectures. You can view this information under Control Panel > Programs and Features. For details, refer https://support.microsoft.com/en-in/help/2977003/the-latest-supported-visual-c-downloads
Check if there is any active remote desktop sessions on your PC.
Open Task Manager.
Check if "NVIDIA Web Helper.exe" application is running.
Under "Services" tab, check if "NvContainerLocalSystem" service is running. If not, right click and select "Start Service" to manually start it.
Still not fixed? Send feedback via GeForce Experience (under GameStream category).
If the problem is not solved, try the following steps: