Hi from glenaurora I have recently installed a 2nd 500GB HD and it will not work on my desktop. It's use is for extra capacity only. The OS is Windows XP home. It is installed via the shared ribbon cable with the original 160GB HD. The ribbon cable is plugged into the secondary mother board connector(this is the way it's always been) The 500GB HD(New) is connected to power and the grey 40 pin connector and the 160GB HD(Old) connected to the black 40 pin connector The old HD is set to "master" and the new HD is set to "slave" When both are connected I get a message upon boot up telling me there is no OS installed. When I disconnect the 500GB HD from power and the ribbon cable everything works fine. Could this be a matter of formatting the new HD or does it need to be connected seperately to the primary ribbon cable connector on the mother board? It only lists HD :C and at no time lists the other HD.