I'm sorry to hear that you're having a problem with your set.
Unfortunately, I'm unable to diagnose sets without being able to inspect them. The power supply is located inside of the TV's cover, and changing out the power cord will likely not fix it, if that's even the diagnosis.
I'd recommend having someone come out and inspect the unit - being able to demonstrate the problem for the technician would help, so having the TV warmed up would be recommended if you go that route.
I have a Samsung LCD that begins making a very high-pitched noise about 20 minutes after the TV is on. I think it is about when the TV starts warming up. Anyone have any ideas what this might be?
I looked online and it said something about a bad power supply...does that just mean a new power cord from the TV to the source of power?