This computer is an HP Pavillion yes. It runs on XP. My other computer is a Dell Inspiron with Vista, unfortunately enough, on it.
My graphics card is an NVidia, but the hard drive in this was sent to me blank when HP repaired an issue with it. It used to run Vista so I stuck an OEM of XP in when I saw the hard drive no longer had an OS on it.
Maybe the problem lies within there?