Stuck on Welcome Screen

I updated to 10.10.3, opened the new Photos app and everything looked and worked great. All my photos appeared to copy over from iPhoto and I was able to browse them and play around with all the new features.

Fast forward a couple days later and when I open the Photos app I'm see the Welcome screen with the get started button. It's like I just installed the Photos app for the first time...which is weird, because I already went through the getting started pages a couple days ago. When I click the getting started button I see a spinner underneath it that's been going for hours.

Not sure what to do now. Thought I'd restart the computer to see if that helps, but when I try to restart I get a window that says that Photos can quit because it's creating or opening a library, but like I mentioned, the spinner has been going for hours...much longer than when I originally updated and opened the Photos app the first time (when it actually worked).

Any help is appreciated.