If you have lost the picture totally and can't see the menu, turn off the power from PS3 from power button and then power it on by pressing power button continuously about 10-15 seconds.
It should then reset the settings and find the HDMI device if you have it connected. You may have to tune some settings still manually for best results (for 720p tv / for optical audio / dual audio etc.).
Basic setting should be found normally automatically. If you are using some kind of HDMI selectors etc., remember to switch them to PS3 position before resetting video setting so PS3 can recognize the display easily.