Question [Q] my note 2 does not open

hi all i am new in there but i want to help me about my note 2.A few days ago my note 2 was closed and i can not open again i try a lot of time.Some of telephone seller says we can fix it 150 $ but its so many money for it please help me about it
problem:
last days of my telephone she was get slow
i dont understand why.. One day i see its name on the screen and can not open
How can i fix her ?