Doesn't boot with GPU after Driver installation.

OS is Yosemite (10.10.5)
1. I installed NVIDIA Web Drivers, 4K fully Works!
2. Installed Drivers with Multibeast --> Cant Boot without nv_disable=1
GPU is a Gigabyte GTX 960 Windforce 4GB

With El Capitan everythingworked fine except FCPX (What i need)

What could be the Problem?

Thank you

Drivers from this Post:
http://www.tonymacx86.com/yosemite-...i-using-hd4600-chimera-multibeast-method.html

I very much doubt your PC-Mac is an iMac. Update your profile with your actual hardware, otherwise cannot advise you. Not enough info.
List steps taken for installation, one by one - what did you do to get to this point?