I had called up Orion support a few years ago to get my SkyQuest XT12G working, and they gave me great instructions.  However, things have changed a bit for Starry Night Pro Plus 7, so I thought I'd post the updated instructions here to help folks out.  I never posted the instructions for SNPP6, which I hogged all to myself, but I can post it if people need me to.

First know this:  It was confirmed to me by Orion support that all Orion GoTo telescopes are controlled by the Celestron control set, so you will be able to control your Orion telescope in any software product that includes Celestron telescope support.  Keep in mind, however, that you will still need to add an additional ASCOM driver (it was included in SNP6 as Celestron NexStar 8, but not included in SNP7) and also enter the specs from your specific scope on top of that, so keep reading.

Starry Night Pro Plus 7 scope control for the Orion SkyQuest XT12G (and all other Orion GoTo telescopes):

1. RS232 cable required for Starry Night Pro Plus 7 usability, part#52419 from Orion.
2. Orion support says same DB9 to USB (RS232-USB) cable available from Radio Shack, known to work (install by directions).
3. Collimate and align the scope as normal and accurately as possible
4. Plug everything in (scope, laptop)
5. Install the additional ASCOM "Celestron Unified" telescope driver (separate download from ASCOM site)
6. In Starry Night, go to Telescope tab/panel (left side of screen, after enabling via View/Show Telescope Panel):
   1. “Configure” button
   2. Select “Celestron Telescope Driver"
   3. Click on Properties, and then select “Advanced Setup" checkbox as the scope model
   4. Select proper com port that was assigned to the RS232/USB cable
   5. Scope Numbers to enter specific to the Orion SkyQuest XT12G:

                                    i.      Aperture:  305mm (get the correct number for your specific scope)

                                    ii.      Focal:  1500mm (get the correct number for your specific scope)

                                    iii.      Obstruction:  70mm (get the correct number for your specific scope)

                                    iv.     Set track mode to AltAz (or whatever track mode your scope uses)

                    6.  Enter correct site/GPS location info

                    7.  Click OK

        7.  Once it’s all entered, click on “Connect” in main panel.

        8.  Once connected, right-click on objects and select either “Center” or “Go To” to slew the scope to target and start tracking.

Look up your scope's specs on Orion's web site.  For example:  Orion SkyQuest XT12G Specs

Bonus:  I have also developed a cell phone/tablet app that quickly gives you GPS coordinates in both ASCOM and Orion GoTo formats (which are annoyingly different).  The app is called "Quick GPS for Orion GoTo Telescopes".  Look for the app on Google Play for Android devices.   Sorry, I don't support Apple's products or their greedy control-freak developer restrictions.