Why my computer wont sell?

That's a very fair price. Maybe people don't want to invest in "old" tech and are dissuaded when they see something like the 4870, when they're in the 6000 series now. Well 2 4870's are the equivalent of an hd 5870 so if you add the crossfire 4870 it'll be much more sellable. If you do that i'd raise the price to like $550 though.