I just bought a refurbished HP Pavilion 9780c with AMD Athlon 900. I had to install a new Ethernet PCI card so I opened it, placed the card and closed it and then I press the power button the PC does not start. What is strange is that the power unit van makes 2-3 rounds and then stops. I am sure I have connected all the cables properly. Does anybody have any clues to what the possible problem could be?