after ~20 Minutes audio output stops completely

in 70% of the time, after a skirmish against the AI in single player the game speed just pauses. No "Won" Overlay is displayed. Pressing ESC shows the menu. Once "Surrender" is pressed nothing happens. Once agein pressing ESC displays just "Continue","Options" and "Exit". After pressing "Exit" the menu just disappears and nothing else happens. The only way to Exit the Game is by killing the Process.