Hi there, Welcome to the Forum.

Hmm, you say that after you start any game that the sound no longer works, but it will work once you reboot.  I'm thinking that this problem may be related to your Windows Audio Service.

When you boot up, check your Windows Audio Service to see if it is running.  To do this click start, then go to Run, the type  services.msc   then hit enter.   





Scroll down and look for the service named "Windows Audio" and verify that it is running (it should say STARTED)





Then, start a game.    Now, go back to the services and see if "Windows Audio" is still running (it should still say STARTED).   


Check that out and post back to let me know what your findings were...