Ubuntu 12.04 will not boot and grub does not boot it anymore

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http://askubuntu.com – I have a computer with 3 hard drives on it. I have Ubuntu 12.04 on my newest and biggest hard drive and windows xp on my 2nd hard drive and a old version of Ubuntu 7.04 on the third hard drive. Everything was working perfectly and I was using Grub to choose between the different systems. I was using windows xp and it automatically did some upgrades and the next time I tried to use windows xp, it would not not boot up. So I tried using the windows xp cd to repair it and I used a dos command like a dltmbr or something simalar to it and when I tried to boot into ubuntu 12.04 it would not boot! I (HowTos)