Dell Inspiron 15 3000 sometimes won't start-up properly

I purchased a brand new Dell Inspiron 15 3000 2 months before.

This system is having Windows 8.1 OS

I'm facing the start up problem from last month. Problem is

1. Sometimes when I pressed the power button system won't start. Black screen comes then it won't boot

2. Sometimes when I pressed the power button system will boot up to password screen, if I entered the password and hit the enter key, again Black screen comes.

3. Sometimes shutdown is not possible.

      a. I tried to shutdown by using mouse (Start -> Power Options -> Shut down) it won't take the command

       b. I tried to shutdown by using keyboard (Pressing Alt+F4) it won't take the command itself

Please post a solution for this.