My flat panel screen just flashes on for a second, then the LED power button flashes green, on and off...checked all connections - nothing loose, nothing changed in years...

Check that you have other operating channels. This may indicate that your tuner board is not working, and that you cannot process channel signals for your TV. Likely you have adequate power if the LED is green.

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit stage inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power led, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating, to many popular brand TVs and other devices. Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given.

Try changing the input device to something you are sure, works such as a DVD player.

Switch off TV manually, switch off power, remove plug and retry after 48 hours.

If problem persists, please refer it to a qualified service technician.

U have sound but no picture?Picture does flashes a few sec?Yes,than those 2 long LCD inverter boards are dead.Tries websites like Shopjimmy.com,Ebay.com to buy those 2 long LCD inverter boards for the replacement.

Check the four transistors (c5707/5706) in the inverter section for shorts, board looks like this? http://www.lcdrepair.us/e152-e153fpb-inverter-power.html

Power supply board is dead,replaced the power supply board will get power.

Check the Lamp if no picture, audio may be present. Screen is completely dark. Lamp LED flashes 2X every 5 seconds, Power LED flashes GREEN for 140 seconds then flashes RED.
Check the ballast if no picture, audio may be present. Screen is completely dark. Lamp LED flashes 3X every 5 seconds, Power LED flashes GREEN for 140 seconds then flashes RED.

I have a similar problem.
Switching the screen off (front panel button) and on again after waiting a few seconds fixes it.
This is a recent problem, so I'm expecting it to get worse and worse until one day!!!!!!

ITS BROKE - YOU HAVE TO GET IT FIXED OR THROW IT OUT. SAME THING HAPPENED TO US -UNDER WARRANTY BUT WE HAVE TO PAY THE $80 TO SHIP IT TO THEM. WHAT A FARSE.

My Hitachi Model 50V500 led's ligths temperature and lamp blink when power is turn on.Have no picture or sound, followed the reconmended procedure disconnected power
for 30 seconds and reconnected.