Is the Lamp ok? Go to the rear of the set and turn on the set with your remote while looking at the vent slats. If you can see a bright light through the vent slats then your Lamp is working. If the lamp is on and you have sound and no pix, then the Digital bd is in what we call "Video Mute" and will have to be replaced. Also make sure that the Lamp Door is installed and the screws are tight
also check to ensure the following.....
1. re-seating the DVI cable on both sides
2. Check to be sure the lamp door sensor is closing (that is not your issue but i thought i would post the complete answer)
3. Check colorwheel is spinning up (should be a low hum, and not sound like a fan)
*** it is very possible it is a failed colorwheel, but the set should go into shutdown, so it is probably not the issue.
4. If the set has sound but no picture replace DMD board....


If the set is working and then just stops working best bet is the DMD ( i would not replace just the dmd it is cheaper in most cases and much easier to replace the lightengine) but if the set just is not working and just failed and is now always not working best bet is the digital board.

If you have an osciloscope you can measure the video signal from the Digital board and see if it is present with the no picture, if it is then it is a bad DMD but if the video signal disappears of then you have a failed Digital board. You can not us a computer USB scope, they can not read most of the data from the digital board since they use multiple scan rates and wont trigger on them for some reason, a old school scope works best i have found, or one of those new LCD scopes that have an auto trigger work well i have found that it is all i use anymore.

you can find a service manual with schematics at a very cheap price at ebay......

regards
iversh