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.