Newbie question

[Mark Gargan]

Hi folks,
    I've just recently started using Tomcat and so far it's been giving me
a bit of hassle. At first it couldn't find a class in the web-inf/classes
directory of an application and then it just wouldn't startup with no log
explanation. So I rebuilt it and now anytime I go to try any of the examples
or indeed any of my own applications I get the error

"HTTP Status 503 - This application is not currently available
 The requested service (This application is not currently available) is not
 currently available."

Has anyone come across this and been able to get over it? Any help would be
greatly appreciated.

Thanks,
Mark.