I am also not trying to beat up on you, but cody is correct. While you may have spent a bundle on your computer when it was new, the value drops very rapidly. The posted specs of the machine, DDR2, only 4 GB memory, and so on kind of tell us it's "last years" model.
You'd be a lot better off looking for a used reef system or components and paying cash. If your handy, consider a lot of DIY projects for your new reef.