[ubuntu] "No boot disk has been detected" even after reinstalling grub

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http://ubuntuforums.org – I just moved and decided to keep my old hard drive with Precise installed on the first partition (now sda1) and my /home on sda3 (swap in the middle) but to leave my old computer and put my hard drive into a new one. I have not I swapped my hard drive for the one that came with the computer (it had Windows installed) and tried to boot up but got the message "ERROR: No boot disk has been detected or the disk has failed." I've tried a number of things to solve this problem, including reinstalling grub several times (which was more complicated than it sounds, because apparently with my (Hardware)