My son has a thing with digital stuff, especially gadgets with screen, for him every screen is a touch screen. He loves pressing stuff and operating things. Few days ago, during one of his setting quests, he messed up with my PS# and it went to 576p settings and stuck there. The TV wont display anything from the PlayStation. I tried several options to restore it with no success. Then I decided to connect it to a computer screen, still got no respond.
Frustrated and not knowing what to do next, I started holding down switches to randomly try resetting something. Then I held a power switch for few seconds, then I heard a second beep after the usual first one. Then the TV screen displayed from PS3 asking to set the resolution for it. After I selected the correct resolution, everything went back to normal.
Just in case you encounter the same situation, you may try holding the power switch for few seconds, after you hear the second beep after the usual first one, then remove your finger and things should be happening on the screen.
Hope this helps.