Moving Outlook 2010 PST files to a new location
Close Outlook.
Go into Control Panel>User Accounts>Mail>Data Files and add the PST (Open File Location and pick the location of the old one, wherever you moved it to). Then set it to the default.
After you re-open Outlook, you can then remove the new, empty one back in Control Panel>User Accounts>Mail>Data Files (you will probably have to close Outlook again, but it was important that you opened it once). Alternatively, in the navigation pane, right-click it and just close it.