Captain caps strikes again!
Sounds like your tv is actually getting too warm.
Is your tv located in an enclosed space?
How old is the TV?
Has is ever been damaged before?
If the TV is under a year old then I would suggest you take it to your store for a manufacturers warranty repair, this will be free.
If the TV is over a year old then I would contact the store of purchase to discuss options. PC world/curry's do an OoWA (out of warranty assessment); basically you pay £200 (iirc) and if the defect is determined as a manufacturers fault then you are refunded and will have a free repair; this may be subject to perticular makes though.
In all honest however if the tv is over a year old then just buy a new one.... it isnt worth the hastle.