ubuntu dual boot windows 7 for vaio grub terminal problem

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http://askubuntu.com – I've followed the instructions for the ubuntu windows installer for my Sony Vaio laptop(SVT131A11M) and once the system restarted it gave me an option to boot into Win7 or Ubuntu. But when I shut down the machine and I choose to boot in to Ubuntu I select that option and it now takes me to the GNU GRUB termial with a grub> prompt. I'm able to boot into Win7 ok but cant boot into Ubunti any longer. I'm confused why this happens when it let me initially boot into Ubuntu. Please help (HowTos)