You should be able to go to the screen resolution settings click on the external monitor 2 and remove it, you may have to plug it in first, remove so you just have 1 set as primary monitor.
You may have to go into Ati/AMD or NVidia settings.

I have ADSR on C: and ACID Loops on D:\ added to the ADSR Library, sometimes it has to wake the D: up from sleep that will delay at first but once spinning you should be right.