This could get long.  I have a 980ti hybrid. Got a second one yesterday for a good price online. New in sealed box.

Uninstalled NVidia drivers and put in new card. MOBO is a Z77 Asrock OC Formula. 850 watt OCZ ZX power supply with 4 PCIE 6/2 cables.

Upon boot up windows is not seeing the second card in device manager. BTW 10 months ago I was running 970's in SLI on the same hardware but I cannot remember whether that was Win 7 or Win 10 (Fresh install not upgrade path).

Here is what I did to trouble shoot. Canned air to see if something was in the pcie slot.

In the second slot the card DOES get power. Led's, fan, AIO fan and pump all run.

Reversed cards. Both cards work in top slot while neither is seen in device manager in second slot. Uninstalled drivers and ran DDU. Inserted cards booted to basic VGA driver and then installed Nvidia drivers and no go. Tried this with one card and both. My mobo has a physical switch to turn off/on the pcie slot. It is on or else the card would not get power at all. In bios changed back and forth from gen 3 and auto. Ran the 970's last year on Gen 3.

Put both cards in second slot leaving top empty and no go. I get 4 or five quick beeps from bios that I think is no VGA detected but I am not sure. Tried 2 or 3 versions of Nvidia drivers no go.

Changed the PCIE cables from the card in top slot to bottom slot - no go.

Here are the things I have NOT tried because I got too tired.

Try the second card in the bottom (3rd) pcie slot after removing usb cables etc. This would only run at 4x but I at could see if it would show up in device manager. Should of done that quicker but my brain was foggy as I was frustrated and very tired.

When I installed Win 10 I did not install any chipset drivers as the Asrock website still showed old stuff and Windows looked like it put in the correct stuff. Besides this issue my pc runs great. I5 3570 at 4.2, 16 gigs ram, SoundBlaster Z in PCIE 1x slot above pcie slot 1.

Remember, I did have 970's in SLI using the exact same hardware until last October when I got the first 980ti. Just not sure if it was Win & or 10. I think 7. I did uninstall the drivers when I switched.

Sidenote: Years ago I remember having to go into the registry to delete some device ID stuff because I could not get a new GPU seen in device manager on the second slot. Maybe 7950's after my 5970 but I cannot remember. Any thoughts on this!

I am at work till 5:30 CST in U.S before I can try any other fixes. First thing is 3rd pcie slot to see if slot 2 went bad. Weird since it was good a year ago.

I am very sorry that this took so long but I wanted to give as much information as I could so that the first 5 posts are not try this and try that when I already did.

IF the 3rd slot works in device manager I assume slot 2 is bad unless it is some weird registry device conflict I mentioned before.

I really do not want to reinstall windows but it is on ssd so it should not be to bad. I would go bonkers if I did a reinstall and it still did not work.

If the card gets power and looks like it works would the slot be bad????

Thanks for any ideas.

No Lucid,  Tried it in middle by itself. Neither card works but I did use that slot by itself when I had a 5970.  It is weird that it gets power but no device manager comes up. Not even an unknown device.  I am going to try it in slot 3 pcie - that is 4x but at least I can see if windows see's it.  I am thinking of uninstalling reinstalling chipset drivers.  Some people have said power supply but why would it run 970's in sli in crisis 3 at 7680x1440 and not even boot the 980ti's in sli?
 
Thanks for the reply by the way!  I do not see in bios where it says which slot speed it is running 2x/3x.  I just see where I can set 2x/3x/auto for each slot but no indication what each slot is running at.  I think if I take a couple of the USB front case cables out I may be able to get it in bottom slot.
 
 

Install Asrock Win 10 software drivers
 
http://www.asrock.com/mb/Intel/Z77%20OC%20Formula/?cat=Download&os=Win1064
 

Sajin
Make sure sli/xfire supplementary power connector is connected.
 

 

Thanks! was already connected.

That is a strange tail; I'll add to my list of you can't make this stuff up.
 
Usually: clear CMOS, load default optimized BIOS, save, power off loads new hardware, reboot, turn fast boot OFF, save, reboot ----> causes the BIOS to reexamine the MB for new hardware.
 
Glad you are all sorted out and SLI is functioning