Lost previously okay SQL Server connection

I'm using SQL Server Management Studio to access Server 2008 databases on our LAN server. No problems until (we suspect) a reinstallation of Kaspersky anti-virus 2012 (single PC version) on the server appears to have cut the SQL access. Error message copied below. We've explored the assistance available at <go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=-1&LinkId=20476> but haven't resolved the problem. All suggestions are most welcome. Greg TITLE: Connect to Server ------------------------------ Cannot connect to FS01\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. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1) For help, click: http://go.microsoft.com/fwlink?Prod... ------------------------------ BUTTONS: OK ------------------------------