You need to cut power to the displays for 10-15 minutes for some dumbass reason, it should work from then on. You may also need a BIOS update for the video card.Can confirm the 980 is goofy as fuck for DP. I can't actually get my computer to boot if I have my two monitors connected only via DP; neither screen comes on, and it's not even posting or something cause if you ctrl+alt+del it it just reboots instantly. It works 100% fine though if I leave one monitor connected via DP+DVI, then manually change the monitor input from DVI to DP once it's booted to the login screen.
Makes no fucking sense at all to me and I've kind of resigned myself to just live with it until I build something new.
Go to System Information in Nvidia settings, "If the version number is older than 84.04.31.00.00, please contact your board manufacturer for an updated video BIOS update. "