I had this problem. My GTX 780 was detected but was getting this message. I'd seen people doing full uninstalls/reinstalls to solve the issue, but were losing settings. Though, I was able to resolve the problem while keeping my custom settings intact. Hope this will help others resolve the issue.
1.) Close Geforce Experience if open.
2.) Go into Device Manager -> Display Adapters -> Nvidia Geforce GTX XXX
Then disable it (This will make the computer pop back into standard VGA,
But won't actually uninstall anything).
3.) Restart Geforce Experience.
4.) Reinstall the drivers from there using the 'Express' option.
(Express should keep any custom settings you have)
6.) Start Geforce Experience. It should now ask you if you want to scan for games.
Hopefully it's working now.