All I did was reactivate a plugin (Pinterest button) and now I get this message when I try to login:
Warning: Missing argument 2 for wp_widget() in /home/vg004web00/53/32/3003253/web/wp-includes/widgets.php on line 76
Warning: Cannot modify header information - headers already sent by (output started at /home/vg004web00/53/32/3003253/web/wp-includes/widgets.php:76) in /home/vg004web00/53/32/3003253/web/wp-includes/pluggable.php on line 897
I have a backup, but it's not very recent. If I can't get in, it's a lesson learned the hard way, I guess.