Homepage shows up after clicking any link - routing problem?

[eluser]Unknown[/eluser]
Hi,

My website (http://myjugaad.in/) is hosted on a shared hosting account (hostgater). Till last week it was working perfectly but now suddenly there is a very funny error showing up. If you go to http://myjugaad.in/ and click any link, it just reloads the homepage. For example, http://myjugaad.in/about shows homepage when it should show the about page. However, if you insert index.php in he URL, the right page is shown (http://myjugaad.in/index.php/about). Earlier every URL was accessible without index.php

Now how can suddenly this thing could change? I have checked .htaccess, folder permissions, script permissions, everything seems to be fine.

Please help.

-Paras