Need Help Converting My Ps3 Display/audio Settings!?

I went to my grandparents and have a 1080i plasma screen, I used an HDMI cable for audio and visual display. Now I'm back home, and unfortunately I forgot my audio conversion and display settings back to the AV cables, and all I have is a 1080i HDTV, not plasma. When I try to use HDMI on my HDTV, it only shows a blank screen with some gray fuzz things across the screen. HELP!