What is it with localhost:3000 ???

I am on Windows, I got Instant Rails v1.3a (as mentioned in the book
by Patrick Lenz- "Build your own Ruby on Rails web applications").
Now, going through the tutorial, I created new app shovell, then
started WEBrick. When entered http://localhost:3000/ for the first
time, it was working.
Then, after restarting, I again fired up WEBrick, but this time
localhost is not working.
After 10 minutes, Instant Rails is giving the message= Instant Rails:
Server starting

What is this ??

Had a similar problem when i started. turned out i had some errors in
evironment.rb or something and that prevented the server from
correctly starting an loading rails.

did you change anything in environment.rb or another config file?