Although you should contact the dealer who supplied the Plasma TV first, it will help them to help you if you also contact Hitachi customer support and explain the problem.
Major manufacturer's are sympathetic to cases of early failure of Plasma & LCD TV's just outside the warranty and will often pay part or all of the repair cost.
Usually, the manufacturer will not allow a dealer to register a complaint on the customers behalf, you must do this yourself.
So get the ball rolling with the manufacturer after contacting the dealer.
Cobweb, November 2007