TYPO3: Backend login redirects to index.php

Recently I have been having some problems with my typo3 installation on my webhosting. One of those problems is, that whenever I login to backend I get redirected to index.php and not the backend. The admin panel is shown on the index.php indicating that the it logs in successfully but then why can't I go to the backend interface.

I have tried several things, like clearing the be_sessions table in the database, clearing the browser cookies, deleting the cache, testing on other web browsers etc. but still no luck.

I am using TYPO3 4.6. Any help will be highly appreciated. Thanks :)