PS3 picture problem

[Jet Set UNITED]

I recently took my PS3 round to my Bro's house, he's got a 1080p ready TV so we jacked the PS3 up to that resolution. But when I went home and put it back into my 720p native TV.... nothing
I've tried hooking it up with the standard AV cable and still no picture. Any tips on how to get it back to 720p?

(My brother lives over 2 hours away so going back and reduced the resolution on his TV is a last-stop option.)

[Zatoichi_Samurai]

hold down the power button when you switch on the ps3, it will go to the default video set up screen.

[Strolls]

Hold it down for 5 seconds (more like 4 by my count) until you hear the second beep.