Sorry for my late answer,
First my specs:
System: Alienware M15X
RAM: 16GB 1333
HDD: Internal SSD Hyper X Kingston 480GB + Internal 2TB HDD Samsung (I replace the optical drive)
Processor: Core i7 940XM
Graphics: nVidia 970M 6GB (Dell VBIOS) MXM
No Optimus (No integrated Intel Card).
I have tried several setups on my Alienware, but only this works with this:
First:
Boot Installer with nv_disable=1
Install Yosemite 10.10.1
Boot OSX with nv_disable=1 and GraphicsEnabler=Yes and continue the first steps in Yosemite 10.10.1 (You will have video, but no acceleration)
Install Combo Update 10.10.3 and reboot (Boot again with nv_disable=1 and GraphicsEnabler=Yes)
Install WebDriver-346.01.02f02.pkg, ONLY THIS VERSIÓN WORKS FOR ME
Reboot, boot with: nvda_drv=1 And GraphicsEnabler=Yes (set this on Clover or Chameleon)
Enjoy 970M/980M
Yesterday I tried El Capitan, but no luck, same black screen or reboot.
Please let me know your comments, and do not use any other version of Yosemite or nVidia Web Drivers.
Downloads:
Nvidia Web Drivers:
http://www.nvidia.com/download/driverResults.aspx/84213/en-us
Combo Update:
https://support.apple.com/kb/dl1804?locale=es_US