I'm experiencing a boot/reboot quirk similar to, yet somewhat different from others posted here.

I have two Western Digital "Passport" external USB2 drives (160GB and 320GB) with Ubuntu 11.10 installed.

The BIOS on my laptop is set to boot USB drives before the internal drive, and it works well.

Either drive will cold-boot Ubuntu 11.10 perfectly.

However, at times the computer must be restarted (warm boot) to have software updates or other changes take effect.

When I warm-boot the computer, the computer goes through its normal shutdown/restart, then the usual BIOS tests, at which time the USB drive is selected momentarily (as normal), and that's when the trouble starts.

I get a "No boot sector found on USB device", and the computer proceeds to boot Windows from the internal drive.

If I press F12 early during the restart sequence (allows manual selection of the boot sequence), USB is still shown before the internal drive on the sequence list (as it should be).

If I highlight "USB" and press ENTER, I still get a "No boot sector..." error message, but the external USB drive then proceeds to boot Ubuntu normally.

I have a third external USB drive (Western Digital 160 GB Media Center) that cold-boots and warm-boots perfectly, so I know everything in the computer is set up properly.

It also tells me Ubuntu is set up correctly on the drives, as all three drives were done identically, and at the same time.

I've tried formatting the Passport drives NTFS and FAT32, but it didn't change anything.

If I power-down the computer, then start it up again, it will boot Ubuntu from either of the Passport drives perfectly - every time.

It's as if during a warm boot the Passport drives are somehow looking for the boot loader in the wrong location on the drive - yet either drives works when booting from a cold start.

Not a show-stopper .. but frustrating.

Computer is a Dell XPS M1530, A12 BIOS (latest), but I don't think the computer plays into the issue because one of the three drives works at all times.

It's only the two WD Passport models at issue here. Thanks!