Default Keep switching off pernamently.

HI
I have problem with my A700.
Its keep switching off after about 1min.
Then is not possible to turn on! I turn on only when I reset with paper clip. Battery are charged at 91%.
Any help?

ps. Tablet is out of standard warranty, but in end of December 2013 beck from acer repair center with new mainboard - so I wonder whether the guarantee should not be extended?