I just got a Xbox 360 arcade(my older pro xbox rrod.
Anyway, i used my cables from my old xbox on my tv and there is audio and the controllers can navigate, but there is no image from my tv.
My tv is a SD Toshiba with composite, s-vid, and 1 component input.
have you tried the bootup button shortcuts to reset video mode? (y or lb or something, i just held everything down). worked for me when i got a vga cable anyway.