I had a similar experience with my Samsung HDTV. After a couple of years, it stopped powering on. I took it to a local dealer for repair, and they wanted $1100 to replace the display panel. Although we paid $2400 for it new, by this time you could get a comparable 40" brand new for $650. So I decided to just take it home and do a little tinkering, as I felt I had nothing to lose.
Since the audio was out as well, I doubted that the display panel was the problem. After doing a little Google research, I found that quite a few people were reporting the same problem with Samsung LCDs. It seems Samsung had done a little cost cutting and used some undersized capacitors on the power board. After a while, they tended to rupture. So I replaced 4 bad capacitors at a cost of about $6 IIRC, and voila, the set powered back up. It's been working perfectly for about 3 years now hence.
Last week I got an email from Samsung notifying me that I was party to a class action settlement for this problem, and that they would reimburse up to $300 towards repair or replacement costs. Too bad I didn't keep that $6 receipt from Radio Shack. I would've turned it in just on principle.
