Sharp Aquos suddenly swtches off and on (and again...)

Hi everybody,
I have the following problem:
after 8 years of work (without any failures) my Sharp Aqous LC-42XL2E suddenly switches off; after abt. 10 - 20 seconds switches on and after some minutes this repeats again.
What is the reason?
Tank you in adnace
Henryk
(Warszawa, Poland)