The Login block has vanished I haven't changed it in /admin/structure/blocks and it is still there.

All that I can think that I installed a few modules to try them out and then disabled them and maybe that caused it.

In any case, my users can't log in and I am in big trouble.

How to go about debugging the problem?  Thanks.  



Update: I am not logged in (I see "Log in or register to post comments"). Even when I load /user/logout the login block is not there (not in the HTML)

The "recent log messages" shows nothing out of the way.
The modules you were experimenting with and then disabled, did you go through the uninstall process?
Also, flush you caches.

I hope that helps.