Doesn't sound too good I'm afraid. You should get a purple screen I think when OS4 boots up (it goes through other colours first). Do the usual checks - disconnect what you don't need (including HDD), check with two different pairs of RAM on their own, that sort of thing.
Boot off the OS4 disk as that's independent of your system. If/when you get a purple screen and a boot, that's when you should look at 3.9 again.