voila la soluce : mais bon c´est en anglais :
When I launch a PS3 game, after the "Playstation 3" logo appears, the screen goes black. The game is loading fine, I just cant see it.
The only way I can regain control of my TV at this point is to tune into the regular TV channels using my TV remote. Only then I can use the input selection button to get back to HDMI. Once I do this, I can see and play the game.