I've been using a 4GB thumbdrive to boot into 8.10 for a while. Recently I rebooted my machine, attempted to boot from the thumbdrive, and it did not work. I briefly got a "Missing Operating System" message before the boot priority fell through to the internal Windows HD.
The only unique thing about what I was doing before I rebooted was that I had plugged in my 3G iPod nano to charge it. This was the first time I'd connected my iPod to ubuntu, but it didn't seem to have any problem. It charged it at least.
So I rebooted and can no longer get my notebook to boot from USB. How might I fix this? Surely nothing was corrupted irrepairably.