SQL Express network access quit working

I have SQL Server 2005 Express installed and running on a Windows XP Professional machine on my local network.  I use 2005 Express because my customer's web hosting plan is SQL Server 2005 based.  For at least a year I've been doing development work using my local server from 3 different workstations also on my network.  Yesterday I started SSMS (2005 Express) from the workstation I normally use, selected my normal login options, and rather than being connected to my local server I received the following error:
TITLE: Connect to Server ------------------------------ Cannot connect to VEXOR\SQLEXPRESS. ------------------------------ ADDITIONAL INFORMATION: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (p ...