dell XPS 13-9350: the key 5, 6, F8 and F9 don't work

Hi All,

Please help me. 

the key 5, 6, F8 and F9 of my dell XPS 13-9350 don't work.

My computer is new. I don't think this is the hardware problem because when sometimes i try to press Ctl + Fn + Alt, they works. 

Thank you very much for your help.

Best Regards,