To get off to an easy start, first step is power. Here is a simple rule, IF YOUR CARD HAS 14 PINS FOR POWER, ALL 14 NEED TO BE CONNECTED ! If it has 12, then 12 need to be connected. These pins are not optional, nor are they mix & match. About once a month we get an email along the lines of "I hooked up one cable and I know it's enough because the fan lights up and spins so the card is defective" In point of fact, the fan will light up and spin with no cables connected, this is a simple failsafe to keep card from catching fire, even if it has troubles. There is another simple failsafe built in that doesn't let the card start up unless all the pins are connected.
The second most common power issue we have is that people can't see that the cables we send can either work as a 6 pin or an 8 pin. The last 2 pins slide off, just have a look. Again, IF YOUR CARD HAS 14 PINS FOR POWER, ALL 14 NEED TO BE CONNECTED ! There are no optional pins, no "only if you feel like it" pins, they all have to be connected.
Some cards will be damaged if you try running them with just one cable connected. Using a PC Dual 6 to 8 adapter with just one side connected will sometimes work, and sometimes not. Better to get the proper setup from us or whoever. Just get the right ones.
High Sierra created some new driver issues. 10.13 and the 10.13.1 update were especially tricky.
A classic sign of the High Sierra trouble is a solid white dock, instead of translucent. This is a partially working driver that will drive you bonkers. This is frequently caused by a partially failed install due to Library install issues. SIP needs to be enabled when you install the drivers.
In the last 2 weeks I have emailed back and forth with three disgruntled customers all convinced their cards were bad. All 3 returned cards are perfectly functional when tested here. This is a massive waste of customer's time and ours.
All Nvidia cards after the GTX 680/780 and Original Titan have required the Web Driver. This is Apple's fault.
People fall into a trap thinking this is some giant puzzle. It isn't.
In "About This Mac" you will see "Version Number" click on this and it will show your "Build Number". So, as an example, 10.13.2 has more than one Build Number. Apple makes a subtle update and doesn't feel like bumping the main number up so they change just the Build Number.
The Web Driver has a simple check in it that compares Build Number. This makes it IMPOSSIBLE to install the wrong driver. ONLY THE RIGHT DRIVER WILL INSTALL OR LOAD. Here is the tricky part to understand for many people. BOTH DRIVERS ARE INSTALLED. One kext loaded at boot looks to see if you have the Web Driver turned on or off. If it is on, it loads the Web Driver. It is is off, it loads the one Apple sent out as OSX Default.
So when Apple issues a Security Update that changes the Build Number from 17C88 to 17C89 the next boot will switch back to the OSX Default Driver. No big deal if you have a GT120 or 8800GT or GTX780 but a completely different story with GTX980Ti or GTX1070, etc.
Anything not covered by OSX Default driver will only work via our EFI on next boot. Typically only one display will work, and the screen redraws will be very choppy, with bands of horizontal black lines coursing up the screen.
It is also possible if someone else uses your machine and does a PRAM reset they will "turn off" the Web Driver. It just needs to be turned back on.
Super easy way to check is to click on that Nvidia Icon in top Menu Bar. It will show which driver is being used.