I know why it happens to me.
When I disconnect my pc from the network, start up excel, excel can't find my
network drive.
It reverts back to some folder on my C: drive.
Here's some code that I keep in a file that's in my XLStart folder.
Option Explicit
Sub auto_open()
'Dim FSO As Scripting.FileSystemObject
Dim FSO As Object
Const myDefaultFolder As String = "U:\my u documents\excel"
'Set FSO = New Scripting.FileSystemObject
Set FSO = CreateObject("scripting.filesystemobject")
With Application
If FSO.FolderExists(folderspec:=myDefaultFolder) Then
.DefaultFilePath = myDefaultFolder
ChDrive myDefaultFolder
ChDir myDefaultFolder
Else
MsgBox "DefaultFilePath not reset, still: " & .DefaultFilePath
End If
End With
ThisWorkbook.Close savechanges:=False
End Sub
If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm