Changing theme breaks database connection

[Lucarella]

Hi everyone, I need help...
The forum worked normally, then I had to set the default theme and the forum broke, with the sentence
Connection Problems
Sorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.

I didn't do anything strange, just change the theme from Halloween to default...
Can I solve it somehow? Maybe change the theme from some file in ftp or from the DB, I don't know....
Thank you

[Diego Andrés]

Try using {forum_url}/index.php?theme=1
It will enable default theme for you.

[Doug Heffernan]

Connection Problems
Sorry, SMF was unable to connect to the database. This may be caused by the server being busy. Please try again later.

A theme change shouldn't cause that error. It can cause display issues but not a connection error. If you didn't change any of the database details, you should contact your host about this.

[Lucarella]

Diego, it was exactly that theme that I was selecting when the problem occurred 

Obviously I too have never seen breakups due to a change of theme, but perhaps it was just a coincidence.
I also opened cpanel and phpmyadmin and everything worked correctly... I don't know what to say...
Then I contacted the hosting, but it asked me for some data that I had forgotten to communicate and in the meantime the forum was back online, even if I had to log in again.

Thank you both