No webapp can be found any longer ?!

Hello !
I am working with websphere 3.5.4 under solaris 2.8.
Since I installed websphere, I have been able to create many Web Applications using the admin console, following the InfoCenter tutorial.
But now I have a big problem.
When I create an application server like usually, I cannot access to the pages and servlets of its directory :
the server is running, and when I type the page URL, nothing happens, until a timeout.
The stdout.txt file of websphere tells :
A Servlet.has.become.permanently.unavailable.for.service
for different entities (Error Reporting Facility, File Serving Enabler, Auto-Invoker, JSP 1.0 Processor).
Has anybody got any idea for help ?
Thanks,
Gaelle.

Shot in the dark...what does stderr.txt report?

Thanks for try and help me !
Well, in fact, there's nothing in stderr, but I no longer get error messages in stdout (it seems so).
The browser keeps looking for the page without ever finding it.
But there's also a strange thing I have noticed about this :
I still have one application server that works "normally", and when it's turned off andI try to reach a file from the webapp, you kno, I get this 'Internal server error' message.
But when I try the same with the new application server I have created, I don't get this 'Internal server error' message, it just keeps looking for the page indefinitly.
This I really don't undersatnd...