Yeah I set the BIOS to boot USB-HDD. I never disconnected the internal hard drive, though. Ill try that.
ah! I forgot to mention that you also need to enable "boot from usb" option or something similar-can't remember clearly...
There is also a bios hot-key that lets you directly select which drive/media you want to boot through. So you don't have to change the boot order every time.
It's different for different bios. Try finding which works for your bios.