I no longer get ddefault page, I get http 500 internal server error
On what page? I see a database connection error, but no 500 errors. Please give us a URL.
In general, a .php page can give a 500 error if the permissions are set "too high". They should be 0755 or 0644. 0777 and 0666 will give you 500 errors.
If that does not work, check any .htaccess files in any directory. Any file that has an line that starts
RewriteRule
should have a line
RewriteBase /
at the top of the file.