I bought a Samsung series 5 notebook and a very strange thing happened: I installed Ubuntu 11.10 from a usb pen drive but when I restarted (I cleared the existing partitions) I stopped being able to boot from any USB device, whatever I change at BIOS, it always goes straight to GRUB2.
Just to add something to the mix, now I can't boot properly after upgrading to Precise (separate question)
Best Answer
Make sure USB drive comes first in the list of boot devices in your BIOS settings. In some BIOSes unplugging the USB drives removes it from the list of boot devices so you need to do this every time you want to boot from USB, with your flash drive plugged in when you open BIOS setup.
Ubuntu, or any other OS, has absolutely no control over the early stages of boot process - basically, your BIOS decides which device to boot from before it invokes GRUB or any code from Ubuntu.