GRUB install error

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http://askubuntu.com – Whenever I try to install Ubuntu, I get a fatal error that reads: 'Executing'grub-install /dev/sda' failed. This is a fatal error.' Its the same as this, but my graphics appear to be running fine. Also, I'm a complete novice at this and really need simple instructions to understand what I'm doing. I've tried booting from a LiveCD and a USB stick. I don't want to dual boot it because its an old computer that I erased XP and plan on only using Linux on it. When I used a USB stick and set the persistent file storage high, I was able to run it, but only as long as the flash drive was plu (HowTos)