We outgrew a few older external USB backup drives, and purchased WD My Passport 1 TB USB 3.0 drives to replace them.
When they are plugged into the front of our G4, it will blink forever after the BIOS (which is current, BTW) and never boot, even though the USB disks are not "bootable" per se.
Our old drives did not exhibit this behaviour (so I don't think it's this type of issue that I've read about other servers.) The old drives were USB 2.0, but this shouldn't make a difference, AFAICT--the specs say all of the G4's USB ports are the same, 2.0, anyway, so I'm not sure how one port would handle a USB 3.0 device better than another.
If we plug the new drives in one of the back slots, it boots fine.
What's the (most likely) cause? My concern is that the front USB port, and possibly the motherboard, might be starting to die.
(We are experiencing other strange issues with them, or were initially, like intermittent file permissions errors despite wide-open ACL on these local drives, but some serverfault users have me convinced they may be coincidental software/security related issues.)
Update: I found that there was a missing SES driver that Western Digital's site was able to provide. I installed this. After that, one of the two drives (which had had less problems so far) I could not get to prevent the server from rebooting using the front port. I plugged in the other one into the front port, which I had reformatted elsewhere, and it also allowed the server to boot. After reformatting again just for equal comparison and doing a backup--which this time had no issues--and restarting, however, the server would not boot with it plugged in. Since I am apparently getting a marked difference between the two drives, I'm wondering if one of the drives has an issue, although I do not exclude the possibility of the USB port or motherboard having issues. Another thing I noticed is that, contrary to the specs which only mention USB 2.0 for all 4 ports, in the BIOS's hardware list, there are 4 USB 1.1 lines and only 1 USB 2.0 line. That adds up to more than the total physical ports that I can see, unless there's an internal one like on a G5, so perhaps that doesn't mean that anything is necessarily running at 1.1.