Has Dell offered any help? As you know, this should be a minor thing to fix and it has been anything but that....
The fact that Ubuntu sees the adapter just fine indicates a software issue. Since you have done all of the typical driver "adjustments" and reloaded the Dell app, the problem may indeed lie elsewhere. Like with your Win 7 install itself.
Do you have any other BT devices that you have tried to conenct to your system? If so, were you successful?