I would like to upgrade my 12 year olds computer. It is an original Compaq 5360 Presario. It is in a mini tower. I would like to upgade the CPU and Mobo, as well as memory. The unit is used mainley for Instant Messaging, and some online gaming sites. Please give some advice that would keep the upgrade around $300.00-$400.00. Your time and advice will be appreciated. Thanks in advance.