The most probably cause of the problemfor your code becoming unresponsive is that it is not able to open the specified map document. This could be because it does not exist; the user logged in does not have permissions to read/write that folder location; or the map document is broken/corrupted.
It should be noted that ESRI no longer supports VBA. Please migrate all your VBA customizations to ArcObjects .NET. You can choose between VB.NET and C#. Please give the following documentation a read to help with the migration:
Migrating VBA Customizations to ArcGIS 10.1