Good evening Catalina and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the error 500 message you are getting. Yikes!
I would love to help you with this topic.
The first thing I would recommend is going through the following guide: http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/
Hopefully that will fix it.
If not, deactivate the Events Calendar Pro and as a first troubleshooting step, could you please provide us with your complete system information in a private reply using the instructions found in the following link?
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Hang in there!
Geoff B.