eyedropper tool and paint bucket locked.

Because this will happen again to you fairly often, I DOUBT you will want to reinstall every time. 

Window > Workspace > Essentials (Default)

When you see those two icons (Eye Dropper and Paint Bucket) with the checkered (barely visible though) little tag to the top left, you're in 3D mode (like Schoeps said).  But you don't have to start a new document.  Just have to change the workspace to Essentials.

Here is what it looks like in 3D mode... Can't do ANYTHING with the bucket.  Was just trying to add a white BG to my logo... couldn't do it.

If you mouse over the Eyedropper Tool and you see "Material Eyedropper Tool" then that means you're in 3D mode.  This happens to a lot of people after or shortly after they first install the new Photoshop because they're like OOOOOOoooooooo 3D?!?!?! Let's try it!!!

You can also see here that the Workspace is set to 3D from the menu.  This limits the tools you're able to use because only certain tools work in 3D mode.

Changing it to Essentials does NOT automatically change the Eyedropper and Paint Bucket back though.  You will have to right click on them and select the respective tools you want to use.

And now you can see that I was able to add the white background to our logo.

Hopefully someone can change THIS to the correct answer so people don't go uninstalling and reinstalling..................... omg.