I have Dell Optiplex 360 with onboard vga,usb,nic. The PCI slots are 3 and are all empty. The screen goes off abruptly and usb mouse and keyboard not responding to clicks or key press whiles there is power on the board processor lights blinking.I have power off manually to start afresh. During booting it says "Alert! Error Initializing PCI express slot 4". The error goes off only if I disable the onboard nic but still the machine goes off abruptly. What is wrong and how do I fix this?