Help Using componenet cables on 360

I have been using my xbox 360 on my samsung 430 series and it was running fine my buddy cam round and gave me 2 HDMI cables for it and i plugged it in and was getting no sound i checked both wires with my PS3 and only one of them worked so i left it on it HMdi and was gonna go back to component on the xbox but now it says no signal no matter what i do but it will work fine on SD red/white/yellow wires does anyone know how to set it back so i can use my component again, its insulting to my TV to be used in standard definition :D

Theres a switch at the base of the cables(the end that goes into the xbox) that says HDTV - SDTV (i think)
Is it set to HDTV??

yea i did that changed when i had to use the red/white/yellow and no joy

i guess you just plug in the the rgb cables and then the white and red for audio? and set it to HDTV because thats what i have now..