If I start my system with a USB HDD or Flash Drive (thumb stick) attached, GRUB fails to load. Particularly, it just hangs with a blank screen. Normally I would disconnect the drive and reboot, and it works fine, but I'd really like to figure out why this is happening. It's been happening for as long as I can remember (from Ubuntu 10.x to 14.x). I tried looking in dmesg but I didn't expect to find anything there, seems like dmesg would only be able to log if the kernel was running, where GRUB would be responsible for starting the kernel.

I am not trying to boot from these external devices at all, but it is somewhat of a nuisance to have to disconnect any external storage each time, or if someone else uses my computer I have to be mindful to not leave them attached so they can boot to another OS without issues.

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    Have you seen if the bios is set to boot from USB? If you have it set to start from USB and the USB HDD has the boot flag yet no system on it it will hang until you restart the system – chj1axr0 Jul 13 '15 at 11:38
  • I know it can, I'll have to check and see what the boot order is currently, but I remember looking at this possibility before. Should USB booting be completely disabled or would it be ok if I just set the order to internal hdd first? – DWils Jul 13 '15 at 16:02
  • Internal HDD should be first. There is no need to completely disable the USB boot – chj1axr0 Jul 13 '15 at 16:06
  • Looks like the order was in fact wrong. It was trying to take the 2nd hdd (internal), then the first, then boot other was on. I removed all drives from the chain and set only the first hdd (removed CD and floppy which aren't even installed so the system won't confuse any externals somehow) and it looks like it's working now. Awesome! If you could make your suggestion into an answer I will mark it as the accepted answer. Thanks again! – DWils Jul 13 '15 at 16:16
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    np glad you got the problem fixed – chj1axr0 Jul 13 '15 at 16:24

Change the internal HDD to the first boot in the bios and You should be able to boot without having to unplug the USB HDD because some (not all) USB HDD have the boot flag on them and without a OS on them they will stall and you will have to reboot the machine.

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