If you’re using SQL Server in Windows XP, you might have problem to start the database service after a long period of unused. You can see error message below log in the error log (check the log directory where you install SQL Server):
The file "C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\master.mdf" is compressed but does not reside in a read-only database or filegroup. The file must be decompressed.
This is resulted by a compression feature of Windows XP, which certain files will be compressed after unused for a period of time. To reconfirm the situation, change directory to data directory and right click on any of the MDF or LDF file. Click Properties, at the bottom of General Tab click the Advance button. You can see the Compress contents to save disk space at the Compress or Encrypt attributes section is ticked.
To solve the problem, untick this feature of all the MDF and LDF files in the Data directory, and your database service should be able to start.