You'll need to ask your host for error log details, a 500 error is very generic and we won't be able to determine what's caused it without error log details.
I checked the logs, no errors
Unless the server is mis-configured there should be logs somewhere for 500 server errors. If you can PM me the HTTP auth and admin login details I can see if it happens for me, but will only be able to guess at a cause without logs.
Seems to be working on the user side. The Admin login is not going through. I PMed you the login info
You seem to be running PHP 5.6, do you know why you're on such an old version? MyBB should run fine on it but 5.6 was released in 2014, I'd recommend PHP 7.4.
Also make sure you've uploaded all the files, /admin/styles/default/login.css seems to be missing, so maybe some other files are missing too which is why it's erroring. Upload the whole /admin folder again.
Apache Version
2.4.52
PHP Version
7.4.27
MySQL Version
5.7.37
Architecture
x86_64
Operating System
linux
The HTTP response headers say "X-Powered-By: PHP/5.6.40", so looks like the site is configured to use an older version.
I will try to upload the files again. Great idea. Sometimes my ftp hiccups. Will get back with you in about 6-7 hours
The above info was from my cpanel
But I think if the /admin/styles/default/login.css is missing, then that would be the next step to take. Thank you so much for your help so far