Danniels
Ok what is the version of Mountain Lion that you downloaded.
And was used to make the UniBeast USB.
I had major issues w 10.8.5 in the video area w nVidia cards.
Especially when booting up .
Used my 10.8.4 to install and it worked. (this will not work w your CPU and MB.)
w my EGA nVidia Card.
Then Combo Updated to 10.8.5 and used the MultiBEast version for that version to install nVidia drivers for 10.8.4. RollBack the video... Or use the nVidia Drivers....for that version of OSX. (10.8.4)
One thing of note is that not all nVidia cards from all manufactures will work... this situation has been around for along time - manufactures make their own Video BIOS which may or may not play nicely w OSX. And can cause lots of issues w Hacks.
YOu may want to split the SSd into two parts and then when you have the base system working w intel video then dupe it to the other partition and boot from 2nd partition to confirm that it works then update one of the partitions for the video as discussed then boot and check that way you can roll back.
Once you have this done and all is working you can delete the 2nd partition and rejoin that to the 1st partition making it whole again (DISK UTILITIES).
Just remembered that your hardware is Haswell ... you will need to use the 10.8.5 as you base OSX version. You will need to install this version for support for HASWELL.
So then I suggest once you have this working on intel video then to roll back the video to 10.8.4
from the version of MultiBeast that has it for 10.8.4 from archives. And use this video drivers for this purpose.
See this link for info on that
http://www.tonymacx86.com/graphics/101270-nvidia-updates-web-drivers-10-8-4-313-01-02f01.html
Also GB earlier posts in this thread are valid to set up the startup switches.