Well, Apple did it again.
A new security update for 10.10.5 that changes the OS build number and breaks the Nvidia Web Driver.
Nvidia will most definitely release a new update very soon, until then you can follow the below instructions and change the value in the NVStartup kext to "14F1505"
I just tried with a 980Ti and it works fine, now to test the same trick with the 10.11.2 update.
But as usual, MUCH BETTER TO WAIT A DAY OR TWO and use the official Nvidia update rather than these hacks.