Start up a random stars game, then select default race which will allow you to enter and screw with every system thats been generated, then under the spacemaster option of the main toolbar click "create sol system'
That will make a new sol system (duh), then make a new player race in that system set up earth with industry etc and , delete the old player race then you should be good to go.
I probably forgot something important, but thats the basic idea.