i hope someone can help. please forgive that this may be quite long i am trying to explain everything.

i have a lg 42LE5900 tv and every now and again the screen goes fully black (appears turned off) but the power indicator light on the tv (the one that turns on and off if you turn the set on or off) is still lit. so am guessing that the tv is not actually turning itself off. i also still have sound but that would be coming via the ss system. this happens with either blu ray player or the sky box. those two are all the tv is mainly used for.

my set up is as follows: LG TV (42LE5900), LG HOME CINEMA WITH SS AND BLURAY PLAYER (HB405SU) , SKY BOX (sky+hd box unsure model).
all are connected via hdmi cables and the optical cable coming from tv to the home cinema box to allow sky box ss.

it seems to only do it (so far) when the tv has been on a long time, such as all day with a movie marathon (a good few of the harry potter movies (there is only 24hours in a day!) or the star trek movies or lord of the rings or game of thrones back to back).

this time i was watching several episodes of game of thrones back to back and (luckily) as soon as the end credits were to play the screen went black. i admit i think the tv had been on most of the day prior to this but this is normal due to the number of people in the family.

i rewound the sky box far enough back (just in case it was a recording issue) and pressed play but i only received sound from the episode i had just been watching and no picture.

then i tried a change of inputs to the dvd player (thats fun to remember to do blind!) this did not solve the problem but i know the dvd was playing as sound via the ss system was being emitted. then i tried switching back to the sky box input and was greeted to the same.

also tried turning off the home cinema at one point as well (by accident pressed wrong button).

i can seem to get picture back with turning the tv off and on via the normal power button on the tv (well this solved it the last time anyways not sure if i power cycled it with the other times or not) however i did sit googleing on my phone for a short time before doing this.
i do know that in prior instances that if left alone the problem does not seem to rectify itself.
does anyone have any ideas?

also i guess more importantly due to the tv being in warranty should i return for a refund / replacement?

Sounds very much like a HDCP issue, this is where the handshake between two components is lost, turning one or both components off then on again normally resumes normal operation.

If it becomes a major issue you will need to find which component is at fault, which can sometimes be difficult, Sky boxes have been known to be at fault, as have some TV's, Sky boxes are sometimes replaced, if it's a known issue for the TV this can sometimes be cured by an update, if not a replacement if within it's warranty.

Awh that makes sense!
i will try the turn on / off again to see if that solves the issue as per last time and hopefully that will nail the problem.

is there a way that i could find out for sure if this is the problem?

would this problem escalate in occurrence basically will it get worse over time? or if it will stay the same i can not complain especially if turn off/ on solves it every once in a blue moon!

i have been having possible issues with my sky box however until i am sure there is a problem i am thinking of leaving this out of this trouble shooting issue with the tv.

can i just clarify with your last statement if you are suggesting a replacement of the sky box or the tv IF it is within warranty?

you havent switched on a power saver option ?

my boys sony tv will switch the screen off but still play the sound if no movement detected in the room

Great idea, however i dont think there is such an option on that tv is there? i thought those sensors were introduced in new tvs?

i will trawl through the tvs menu and check, maybe its set to something like turn off after 9hours or something.

will get back with my results. anyone any other ideas? is it a fault?

Update:
Energy saving is set to off (always was)
And sleep timer is also set to off.
Didn't notice anything else in the menus.
Other ideas?
Oh now my bluray is playing up - great week for me electrically!