Whtie screen doesnt go away: new installation Codeigniter 1.7.1 on Ubuntu 9.0.4

[eluser]Unknown[/eluser]
Need help.
I just downloaded a new CI package from the site. My xampp installation has php 5.3 running on it. This installation works fine one WAMP with the same php5.3 but brings up white screen with ubuntu.

Changed permissions on every folder in the installation but still the problem persists.

need help urgent!!