Ok changed htaccess to bak.htaccess and i get the same error.
This is server side problem, you must contact your web host.
Can I grant root access? or can I check it?
If you have virtual dedicated server (vps) or dedicated server; you will get root access. We use any SSH client (PuTTY for Windows) to connect and use the command line interface.
In any case, if you are using a managed web hosting account or a shared server, it is not your work to fix, web hosting company will fix after you report or ask. In case of unmanaged, you have to do it yourself to fix. For 500 IS error, these might help you :
I am taking you are using a Linux-Apache-MySQL-PHP (LAMP) server with cPanel. For LAMP 500 server error comes exclusively with single standalone PHP file happens mainly due to :
Error in .htaccess file
Misconfigaration in php.ini file
Problem with permission
With cPanel or any web hosting panel with substandard host or cost saving shared hosting packages, it is common to get 500 server errors, If you search in Google, you will lot of people are complaining, because they can not probably employ good 24x7 UNIX experts at that cost.
You yourself did everything rightly when you arrived here, we have made you understand the facts :
text files, html files are loading quite nicely. So Apache2 is running.
We asked you to test with that foo.php inside a subfolder disabling .htaccess. Your .htaccess is not responsible for 500 error.
Other points mentioned in the above linked webpages. But you must inform your web host (if applicable).