update to add as one of my friends done this with his 360 that was not displaying video only sound, the initial walkthrough worked for him and we got the dashboard up, thats when it happened 5 mins into a demo game screen went blank and 3 red lights on console appeared, damn had not happened to me before, so we took the machine apart again made sure everything was inplace and all was as should be, so we turned it on again and it happened again couple of minutes on the dashboard and blank screen again with 3 red lights, so i suggested we left the console powered up this time which we did for approx 10 minutes, then i felt the urge to remove the coins and would you beleive worked perfect, ran it for a bit then played a game for about an hour and still fine, tryed again this morning and worked perfect again.
so the coin fix, fixed the initial missing video but then produced 3 red lights and blank screen, but then leaving console on allowing to heat up slightly for 10 mins whilst coins were still inplace must have applied enough heat and pressure to the chips to set them right again as once all was removed conole was perfect, this was done on an old arcade machine with zephyr board i beleive according to the ampage etc