External Drives won't let iMac to Restart...???

I have three External HDs connected to my iMac. One Firewire800, one firewire400 and one USB 2.0... and everything works great until I restart the iMac, it keep a blue screen stand by forever, and I need to disconect the drives to restart the iMac and everything goes normal again, I always connect the drives after the restart and so on.... Help

Obviously problem selecting boot disk, poor thing is more than a little confused. When you get it going, reconnect drives and go to System Preferences>Startup Disk and make sure the internal drive with the OS is selected.

Alternatively boot holding down the Option key which should give you a selection of the drives to boot from, provided the externals are Apple Partition Map formatted and have an OS on them.

All the external drives are just for backup, they do not have any OS install. Just Documents how the iMac can be confused if only one disk (the internal) is the only that had Leopard Installed?? I mean the only OS that exists reside on the internal drive... also I want to add that if I have just one drive connected the iMac boot normal, if I try individually with each drive the iMac runs fine, but the three at the same time brings the blue hanging screen of death.... can anyone help me here?