What is your exact model number?
Addition: I saw this while trying to research for you. Try resetting up the picture mode an output resolution. (still guessing)
http://forum.ecoustics.com/bbs/messages/2/16307.html
Prepare for "Not Supported Mode" Messages, July 11, 2006
Reviewer: Aquarices (maryland) - See all my reviews
This TV is great.....as long as you're not hooking anything up to it. Want to watch a movie on your progressive scan DVD player? "Not Supported Mode". Want to connect an HD cable box using HDMI/DVI? "Not Supported Mode". Have an Xbox 360 that you want to use as a DVD player? "Not Supported Mode". Ugh. I am so sick of the screen going black with a pop-up box saying "Not Supported Mode" that this TV is going back from whence it came.
I've tried fiddling with different hook-ups and cables for almost a week now and have had no luck. I can hook up the HD cable box with component connections, but not HDMI/DVI. I can play games on my Xbox 360, but can't watch DVDs on it. I can use an old 480i DVD player and it will work fine, but my newer progressive scan will not. All of these work fine on the 2 other (older) HDTV's I've tried them on, so it's nothing on my end, it's the TV. The only reason it gets 2 stars is because the picture is nice. But I can't justify $700 for a TV that isn't compatible with high end gear. You've been warned.
and
5 of 7 people found the following review helpful:
Really disappointed about the "Not supported Mode", December 29, 2006
Reviewer: Genghis Khan (Bay Area, CA) - See all my reviews
I have been buying Japanese brands all my life in believing that Japanese electronics product is simply the best in terms of quality and reliability for general consumers. But I have been hearing really good things about Samsung's line of TV and the contrast ratio of 3000:1 on this TV made me pull the trigger.
I am just very disappointed because the complaint about the "Not supported mode" is very true. It appears that this TV doesn't like to support progressive scan from a progressive scan DVD player. It does fine with HDTV signals which are currently at 720p or 1080i but half of my use of this TV is to watch DVDs on a progressive scan dvd player. Yes, I can still watch DVDs by disabling the progressive mode of the DVD and watching it in 480i. But that's like going backwards 5 years.
And the thing about Xbox 360 makes perfect sense. If you are playing games on it, you are most likely in HD mode so it works, but if you are trying to watch a DVD, then you are in progressive scan mode (480p) so it doesn't work. I am just deeply disappointed in Samsung that they failed me like this on my very first Samsung purchase. This is a basic mode that they overlooked. Who knows what might go wrong next? This TV is going back to the store. The TV itself is very nice actually. Nice sleek look, great picture from HD signals, but it still left a really bad taste in my mouth that Samsung couldn't get one of the most basic things right.