Sugata

There is only one thing (as I know) that would revert your Wordpress website to the default theme: if Wordpress does not find style.css it will change the style to Kubrick.

Now, if you are using WordPress Mobile Edition from Alex King you might have not installed it properly: if you visit your blog from a mobile, it will search for style.css in the wp-content/themes/wp-mobile directory. If you have, as me, forgotten to copy that folder there, now it’s time to do so.