It is the button on the right side of the screen of the Omni. There are 4 buttons and the top button should be used to switch from pc to game mode. But most of the time it does not react.
Or should I push that button when starting up the pc ? When I start up the PC, at a certain time you see a small window on the screen which says "pc mode".
It did work again last evening but I really do not know why it does work and why it doesn't work.