I'm sorry to hear that you're having this issue.
I might suggest calling 800-SAMSUNG to see if they'll help out with the warranty. If it's out of warranty, the repair will likely be out of pocket. Without inspecting the unit, I'm unable to determine what's wrong with it.
I have a 40" Samsung LNT 4071 LCD TV that I purchased in January of 2008. The other day, my wife was watching television when the picture disappeared. It's not completely black, but black with blue bands and thin horizontal and vertical lines. These lines, oddly, change when manipulating the remote control (as in, trying to change the channel, change the volume, go to the setup menu, etc). Sound can be heard.
I have disconnected and reconnected both the cable and DVD HDMI cables numerous times, to no avail. I plugged our other HD television into the cable box and DVD player and everything is fine, so it is definitely the TV.
The TV is out of warranty, but considering it is less than 2 years old (and cost close to $2000 at the time of purchase), this is a pretty shocking development. I have looked on this board and see folks with similar symptoms but haven't seen a reasonable explanation. The fact that similar issues appear to be common is a little frustrating.
I would like to see if it can be repaired for a reasonable amount of money.
I would also like to say that I will most likely never buy a Samsung television again, nor will I recommend the brand to anyone else. I had been wholeheartedly endorsing it to friends and colleagues up until this point.