I have a GTX 680, 980, 1060 and have the latest driver installed but when I try to use ProRender none of them shows up. I uninstalled (2.5) and reinstalled but no change. Had the same issue with (2.4).
sorry my fault i was thinking of Maya not Max
i went ahead and sent this information to the developer team for you.
A few things we can try though in mean time
1.try either re installing 3ds max or reset it to default.
2.Make sure all GPU drivers are up to date
3.uninstall the plugin (Max sure 3ds Max is not running in Task manager, and then reinstall the plugin.
If you had Nvidia gpu in past on this computer this could also cause problems. this is how another user fixed that issue.