"Hi There",
Have you tried "pushing" the AV cable in "firmly". I am "certain" there is a "red" light error if "the" AV cable is not fully "inserted". I just can't remember if it gives a flashing "red" light.
Also can you "borrow" another "AV" cable? Any Composite/"Component"/SCART/"VGA" one will do as they all "use" the same "AV" connection on the back of the "360".
At some point "someone" will recommend that you "wrap" your 360 in a "towel" to make it "RROD", because your "360" will still be "within" the 3 year warranty for that particular "fault".
rp2000
"Edit:" In the "time" it took for me to "type" my "reply" 3 other people asked/answered the same "stuff". It is "possible" the "speech marks" are slowing me "down". But at this point in "time", that is purely "conjecture".