Problem in Starting OS (New Macpro)

Hi,

I Have a New Macpro (Late2013, 32GB Ram, 3.5 6Core, 512GB Flash Storage).

After 1 month, I have a bad error:

when I starting up the system, when the Apple Icon show, the starting bar (Bottom the apple icon) has stopped and the system and OS not running up. I try to Upgrade from Yosemite to El Capitan. after that, the problem has gone, but sometimes (often!) workstation still hang or not shut down when using the OS.

I’m a Music engineer and working with Cubase (Updated to El Capitan version).

I tryed and test everything  : unplug external HDDs, HDMI & thunderbolt ports, but the problem is’t gone.

what should i do?!