can i just say that would be a complete waste. If you plan on getting a rather weak gpu and cpu thats fine but to get a powerful gpu and cpu you'd have to face the motherboard compatability issues and also you could just take the hard drive out of your rig and also us the same case. Youd have to buy a more powerful psu aswell and tbh using the optical drive out of your current rig means your practically half way there. so GPU check - CPU - Check - Optical drive- check - Case - check. all you need is a motherboard, more ram if you need it and your done. So it wouldnt be worth keeping your old rig really.