Can't boot with external firewire drive attached.
I have an iMac 20 inch (mid-2007) running Lion 10.7.3. When the external drive, a WD My Passport Studio 1TB, is attached via the firewire connection, the iMac will not boot at all. It will be stuck at the white screen, if I disconnect the drive, the apple log appears and boot up continues normally. If I try using a USB cable, the problem does not exist, the computer boots normally. The external drive is a Time Machine drive. The external drive has no Recovery HD partition.
Any idea where the problem is ?
Thank you
iMac, Mac OS X (10.7.3)