Hi cathalcom and welcome to Geeks2Go!
The master browser is called the "Computer Browser" in Windows XP and it runs as a service. The service should be set to "Automatic". It's possibly been disabled or set to manual inadvertently, either of which could account for the problem. Many XP users alter the default services settings to stop non-essential ones from wasting resources, but sometimes they get it wrong and stop a vital service from running. It's even possible a badly-behaved Windows 'tuning' utility may have done it.
Go to Start->Run & type services.msc
then press [Enter].
Look down the list of services till you see Computer Browser
Double-click that entry.
Change 'Startup Type' to 'Automatic', then click the 'Start' button within that same Properties box, to start the service.
Now click 'OK' to save the changes.
Hopefully this will fix your problem, and that service will start automatically in future.
Edited by pip22, 08 March 2008 - 02:56 PM.