ALTER DATABASE <Database Name> SET ONLINE
As for how it got offline, someone took it offline either by issuing a ALTER DATABASE statement or by selecting Tasks-Take offline from the context menu in Object Explorer (management studio)
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass