Mac frozen during Bootcamp Windows Installation

I have just made a clean install of my macbook pro unibody late 2013 with OSX El Capitan. I have created a USB stick from a Win7 64bit ISO with Bootcamp Assistant. Then I have downloaded the Bootcamp Support Drivers for my model from the Apple and copied then over the existing ones on the USB.

Bootcamp created the Partition and restarted the Mac. So far everything went fine and the Installer copied all files and finished "Finishing up"

Now the Mac restarts and I hold Option to Select the Bootcamp Partition to start from.

When I press enter the Mac freezes at the Selection Screen, no reaction anymore.

Starting back into OSX works fine.

Any idea what could be the reason for that and how I can finalize the Win7 Installation?

Can I install from Parallels into Bootcamp Partition?