lenovo hangs on boot when usb drive is connected

[Dave Stevens]

I'm using 14.04.2 on a lenovo that I remotely administer. I have an
external drive attached for backups - has .tar.gz files no OS not
bootable. Nonetheless it hangs on boot if the external unit is
connected. I unplug the drive, boots normally, plug in and mount the
drive, things work ok, can do backups etc. The BIOS settings don't seem
to involve a problematic boot setting, just to boot off the primary SATA
drive. Problem is I have to go onsite to reboot and that's awkward, as
is leaving the kernel unpatched.

Ideas appreciated.

Dave