Check the servers error logs. With a 500 error that’s pretty much the only place you’ll be able to find any info about what’s going wrong.
The only thing that I can recommend apart from that would be checking ot seei if you have a .htaccess file set up,and if you do, delete it to see if that makes a difference.
Wouldn’t deleting the .htaccess file cause bigger problems?
On a Windows server, most of the time no.
As you’re running on a Windows server you’d be 99% sure of running IIS instead of Apache. IIS doesn’t recognise the .htaccess file, so there’s no reason to have it there, and it can cause some issues of IIS is trying to do something.