Hi,
I had that problem with my first 360... was playing a game and screen went like half green and then I turned off the 360 nd had audio but no video output.... cables are not the problem, its the console, I can confirm that because I bought a new 360 and i'mn using the AV cables from my old one & works great @ 1080p! It has the new Falcon mobo but from what i'v read within 10-12 months ill probly get 3rod or video prob.... Your only option is to get a new 360 :-( or induce a 3rod somehow and send it to Microsoft if warrenty isnt voided...