If that's all you have in your .htaccess, that's not the problem.
I can access the front page of the site, which I wouldn't be able to do if there was a syntax error in your root .htaccess file.
Similarly, if I try to access
http://www.enjoykalkan.com/wp-admin, I get redirected to the login page, which means that WordPress gets to run and cause the redirect, again this means no syntax error in .htaccess in wp-admin (if there is one).
So your error is likely coming from php code somewhere.
Check your php log file (if you have one) or your apache error file. I would expect to find a syntax error or some other fatal error in those files. With the likelihood of an exact filename and line number causing the problem.
Mike