The name of the discussion is "Isn't starting up (again)", that would be because of a syntax error. The You class should have had red lines going through it in the side bar of the Greenfoot program, so you see to open the editor of the You class and there should be a red squiggly line under the line of code that says
Greenfoot.setWorld(forSale);
then when you hover the mouse over the line, a black box will appear that says "cannot find symbol- variable forSale", it would probably have taken faster to solve if you would have mentioned this.