After MSDE upgrade to SQL 2005, MDF is not found

After upgrading an MSDE 2000 instance to SQL 2005, the database appears to be intact - according to the log file:

2007-08-28 13:51:13.78 spid11s Starting up database 'HysterSuiteMainSQL'.

Then after a system shutdown:

2007-08-28 13:57:43.57 Server SQL Server is terminating because of a system shutdown. This is an informational message only. No user action is required.

It appears the MDF file disappeared mysteriously:

2007-08-28 14:03:11.84 spid51 Starting up database 'HysterSuiteMainSQL'.
2007-08-28 14:03:11.85 spid51 Error: 17207, Severity: 16, State: 1.
2007-08-28 14:03:11.85 spid51 FCB:pen: Operating system error 2(The system cannot find the file specified.) occurred while creating or opening file 'C:\PROGRAM FILES\HYSTER SUITE\MSDE\Data\MSSQL$HS2000\Data\Hyster.mdf'. Diagnose and correct the operating system error, and retry the operation.

Has anyone encountered this issue? Any ideas on what might have gone wrong?

Thanks,

Mike

After upgrading to sql 2005 did you change the startup account of sql 2005 ? if yes may be the startup account might not have modify privilege to the path where the mdf and ldf resides........as the error is explicit that its related to permission.....