I have a G5 1.8 dual core, 4.5gb of ram running OS X 10.4.11. I battled to install 10.5 on it and ended up taking the secondary drive out and sticking it in my mac pro. Eventually managed to format it 'GUID Partition' and got the OS installed. Stuck it back in the G5 and it appears as a startup disk option. But when I select it the machine keeps reverting back to the original 10.4.11. If I disconnect the drive with 10.4.11 I just get the little alternating face and question mark as if I have no drive in the machine. Also tried swapping the drives around the slots as a last ditch attempt that I thought wouldn't work and I was right. Can anyone help? I fired up this machine and stuck a third party airport card in it but in the three years since I used it in anger a lot has changed. I can't get the latest iTunes or Adobe flash played installed and a whole bunch of stuff needs 10.5 or above. Any ideas anyone. I am going to try disconnecting the airport card and I'll come back if it makes a difference. Thanks Phil.