On occasion, multiple installs and removals of PCI cards can corrupt PRAM on the MAC to the point where the system will not boot up. When this symptom occurs, removing the ATTO host bus adapter will not correct the problem. To fix this, the user needs to refresh the PRAM by holding down the "Command", "Option" "P" and "R" keys after hitting the "Power On" button. Continue to hold these buttons down until you here the Mac chime three times. You can now release the keys and allow your system to boot up normally.