After 4 years of great service my tv cuts of by itself. I unplug for a few minutes and plug it back in and it plays for 30 minutes and cuts off again

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

this just happened to us, we tried the reset button, didn't work. we unplugged from surge protector and plugged the tv in the regular wall socket and after a few minutes the green light quit and we were able to turn tv on

tv works for about 2 minutes, then shuts itself off. the red standby light flashes 50 times, then the tv. comes back on for approximetly 2 minutes then goes off again, only to repeat again

Try unplugging the unit for at least one minute and then plug it back in . The unit should reset itself . I will take 20-30 minutes for the guide to repopulate.

Yup, it seems a lamp problem can give a blinking green light over the 10 times (1 - 10 times for diagnostic codes), but in my case rather than replace the bulb if it works for a minute then resets with the green light blinking, do what I did.
Take the lamp out and inspect it, it has breather screens top and bottom, if it cant breath because there clogged with dust, clean them, and you can remove the screens, use q-tips and clean the inside. I saved the cost of a lamp and it's working fine!

if your tv is up high try to lower it mine did the same thing but after i set it closer to the ground it stopped and hasnt done it since..

I would suggest that you guys turn the unit off when this happens, unplug the unit for 30 seconds, plug it back in, and see if this helps. If this does not solve your problem, you should call 1-800-448-2244, so a service center in your local area can be found for further assistance.

bad light engine assembly.......

I have the same problem. The only way to get the TV to come on is to unplug it, but once you get it back on it turns itself off again in a few minutes.