I can appreciate your frustration, but there's actually a reason the PC input is an 'always on' connection.
Last year, the only way for the PC input to enable was to have a pin configuration in the D-Sub (15 pin) monitor cable that grounded, and essentially allowed the computer to tell the television, "Hey, video input signal here! Coming through!". Well, many different manufacturers had different pin configurations, and no standard was set. So certain models of computers and video cards needed to either update the video card or the computer's BIOS - obviously an unpopular choice "just to see video" for many of our customers.
I would answer or help troubleshoot at least one of those a week in 2008, and since the 2009 models have the PC input as an "always on" connection, I've seen few - if any - problems this year regarding 15-pin computer connection issues.
So both the internal tuner, and the PC input are "always on" connections in the Source Menu. I don't know of any way of toggling that option off, unfortunately.
I realize that doesn't give a solution for your situation, but does that help explain a little?
UN46B7100. So when you have something plugged in, say a PS3 its shows up as that port being used and available when the PS3 is turned on. I had my PC hooked up to the TV - so the PC "channel" was available and highlighted. My PC crashed and it is no longer hooked up, but the PC "channel" remains highlighted and available. How do I get rid of it? I have tried plugging a VGA cable and just taking out to no avail. Not so much a big deal, just a little annoying.