First, did you read through this previous thread? http://forums.cnet.com/5208-13973_102-0.html?forumID=146&threadID=319407&messageID=2923093#2923093
How is the TV recognized by the computer? Does it list it as "SAMSUNG" or just a generic PnP monitor? I'm going to guess it's the later, which is a sign of a poor VGA cable.
Anyway, what resolution and refresh rate are you trying? 1920x1080p @ something approximating 60Hz should work -- I say approximating because, on my Mac, 60Hz doesn't work but 59.9Hz does work as a refresh rate.
I've been really happy with this set (my first LCD), but ran into the following problem recently.
I attempted to connect my laptop via the VGA connection on the set and then selected it from the list of sources. Initially, the TV didn't detect a signal from the laptop - I tweaked the video settings on the laptop and got the TV to at least acknowledge the signal, however the TV displayed a "Mode not supported" message.
I've tried multiple laptops, different cables, and a whole bunch of video settings in Windows.
Any ideas?

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