I can help you in fixing above error as I had faced this error in recent past.
You can face above error on any site which may be running on any web server. This is not limited to WordPress only. Please find below the known causes of this error are as below :
1. Plugin and Theme
2. Corrupted .htaccess file
The solutions to fix the error are as below
1. Check Error Log
Easiest thing you can do if you face above error is to check your error log file. You can easily find out a root cause of your problem. By simply checking your error log you can find out if any plugin and theme is causing you above issue.
2 Check corrupted .htaccess file
If you are troubleshooting your Internal Server Error in the WordPress then you must check for your corrupted .htaccess file. You can easily do it by changing the name of your .htaccess file to some other name like .htaccess-test. To just Rename your .htaccess File you must login to your site.