Hello, I have an HP SL4782N 47" LCD TV that I got secondhand. It turns on and works at first with several different inputs, although the screen intermittently flickers. I can head a high pitched sound coming from the back of the TV (not quite as high pitched as the normal high-pitched-TV sound, and more of a buzzing than a ringing). After about a minute, the display goes black. Restarting the TV fixes this at first, but then the problem occurs again, faster each time. When I leave it off for a long time, then try again, it's back to about a minute before going black. Any idea what might be wrong? Maybe it's overheating, or has a power supply issue? I'm trying to think of stuff that might go wrong with this kind of time delay.