Try the following:
Sub unlockall()
For i = 1 To Worksheets.Count
Worksheets(i).Activate
ActiveSheet.Unprotect
Next i
End Sub
If you do want to go down the password route:
Sub unlockall()
For i = 1 To Worksheets.Count
Worksheets(i).Activate
ActiveSheet.Unprotect "My Password"
Next i
End Sub