I installed windows xp back onto my zorin6(ubuntu 12.04) system. I know that I have to repair the mbr to get back onto linux. But my ho Compaq 6730s laptop won't boot from USB, its the same USB I used to install it in the first place. I've tried about everything, I can't do a frugal install either, it just says something like try (HDD0,0) ext4. Any help is appreciated.