Black screen.no cursor.lose connection to server

I m an owner of a Macbook Air Mid 2013,i5,8 Gb Ram,128 SSD, and my computer's screen go to "Black". One time i press by accident the shutdown buttonand my computer was like a brik the keybord was open and i have to restart the computer. After restarting the computer there was a msg in my screen that: the computer closed due to a problem..blablabla!!! In an authorized Apple shop in Greece they told me😁 that its the first time the face something like this.......but they was saying the same things to everyone.

Furthermore the cursor many time is like a ghost..its somewhere in the screen..i can do everything but i can not see him😝

In addition i m using a Synology Nas... and a netgear d6200 a c gateway..after installing 10.9 i m losing connection with nas all the time...i m trying to connect to server by its impossible.. the only solution is to restart the Macbook Air...any ideas?!?!?!?!