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 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.)