Somehow I seemed to have lost my login form? 

Any idea of what would cause the login, new account, and reset password forms to disappear? The tabs are available, but the form fields are goine missing. 

I have looked with the inspector to see if it's being hidden by CSS and there is nothing there. Also, I have tried both /user and /user/login and get the same results with each.

Accepted answer

Thanks to everyone that helped me out on Gitter. 

The problem was that I had removed the Main Page Content block from the default page template at some point. The login form renders in this block and without it, I don't have a login form. 

I restored the Main Page Content block and all is well. 

ANSWER:

Replace the Main Page Content block on the page template. 

Comments

Do you see anything if you use the inspector or view the source of the page? (ie. is it hidden with CSS somehow?)

That was the first thing I checked. I should have indicated that in my original question. As far as I can tell from the inspector, the fields are not rendering.

Thanks to everyone that helped me out on Gitter. 

The problem was that I had removed the Main Page Content block from the default page template at some point. The login form renders in this block and without it, I don't have a login form. 

I restored the Main Page Content block and all is well. 

ANSWER:

Replace the Main Page Content block on the page template.