I upgraded to 2.4.5 from 2.3.3.

Filecheck was proper.

Upgrade went smooth. Now, no front page.

I can get to modules admin and disabled everything but the system module.

I made sure theme was set to default, re-uploaded default theme and updated system module.

I removed the protector folder after the problem showed up.

I get an internal server error when I try to access the home page or the control panel home.

I'm guessing it is something simple, but I can't get it.

Do you have enable the debug modus? I think you have an permission problem.

Debug is turned on but nothing at all shows on the front page.

If I upload a basic index.html file, it displays properly.

This is the error messge:

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@mysite.ca and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Apache/1.3.39 Server at http://www.mysite.ca Port 80.

On the pages I can actually access, there are no errors reported.

You were right Webmystar. Permission problem on the root folder, fixed by my host.