Site gives blank screen on localhost

[eluser]martillo[/eluser]
The only error log I can find is in system/logs

It shows

DEBUG - 2009-01-02 14:31:47 --> Config Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Hooks Class Initialized
DEBUG - 2009-01-02 14:31:47 --> URI Class Initialized
DEBUG - 2009-01-02 14:31:47 --> No URI present. Default controller set.
DEBUG - 2009-01-02 14:31:47 --> Router Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Output Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Input Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Global POST and COOKIE data sanitized
DEBUG - 2009-01-02 14:31:47 --> Language Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Loader Class Initialized
DEBUG - 2009-01-02 14:31:47 --> Database Driver Class Initialized

Then nothing.

The site works on php4 not on php 5.

Are there any more error logs?

Is there a way i can trace code execution? Sorry if that is a daft question. I am new..