If you get 500 internal server error after installing new Joomla theme then most probably the theme ZIP file was compressed with the wrong file permissions (note that the server permissions are different for servers working with SuEXEC php and without). If you get this error with our hosting then those themes are set to work without suexec and require you to do some manual permission changes to change the default settings of this theme and convert it to suexec compatible.

It is easier to contact our support because we have quick shell command to fix it, otherwise you can do it yourself but it may take few minutes and its frustrating job.

To fix the permissions you will have to:
Go to CPanel->Legacy File Manager, or any FTP Client software. When you go to public_html folder see if there are any folders or files with 777 permissions. If there are you will have to change all of them, including the subfolders to:

Folders should be set with 755 (read,write,execute;read,execute;read, execute)
Files should be 644 (read,write; read; read);

Why we run SuExec?
It is much safer to use SuEXEC because each user (you) have access to modify your files by yourself and is restricted from modifying other user's account files. If you don't run suexec then other users on the same servers as well as internet users may write on your files and inject you with viruses and etc. Our systems are Safe!

Please contact our tech support team via support ticket and we can fix the permissions quickly.

The Maiahost Support Team.