Question : Cannot open user default database  SQL Server  error 4064

Sql 2005
Windows 2003 R2
Was attempting to take a database  offline. It hung for some time and activity monitor showed
a connection. Cancelled the take offline dialog box.
Started getting messages about not connected.
Closed Enterprise manager. Reopened, same.
Restarted server.
Finally got the server connected in Management studio, but the database that I was trying to take off line is now  offline and any attempt to look at properties of bring it online give the same  4064 error

Now all I get is this :
Management studio
Cannot show requested dialog
Failed to connect to server
Login failed for user sa  ( SQL Server  error 4064)
But I can open tables is various databases.
FIrst priority it to  bring the offline DB online
The master db is there.

Tried this :
C:\> sqlcmd -E -d master
1> ALTER LOGIN [BUILTIN\Administrators] WITH DEFAULT_DATABASE=master
2> GO

Any ideas would be appreciated
Thanks

Answer : Cannot open user default database  SQL Server  error 4064

are you able to connect to any other databases ?.
say master, model etc other than the one having problem.

try  bringing online from master.
alter database set online