have your ps3 OFF- then HOLD the power button down until it beeps and it will restore it to the default TV setting.. if this does not work then your screwed , i FKED my ps3 before the same way..
word of advice , if your ps3 freezes DONT turn it off from the back!! ESPECIALLY if the HDD light is flashing.. i did this before and it killed my ps3, cost me 150$ and two weeks of no ps3.. better call sony and get that service box sent to you, takes 3-4 days just to get it..