The game runs great once your inside using Vista. I actually found it runs better than on my old computer but that might be because I have much better computer.
I also had the same problem being able to run horizons.exe after cutting off the computer and restarting.
Unfortunately, to fix it I had to totally uninstall horizons and delete the folder off the C drive.
I then followed everything as before and logged in just fine.
I guess we have to keep our computers running for now!