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I have a lenovo z570, and I installed Ubuntu 12.04 alongside Windows 7. Recently all my games that I've been playing stop responding due to a AppCrash.

I searched for the error on Google and they said it had something to do with Ubuntu. So I deleted the partition. After restarting my laptop i get the "unknown filesystem" grub rescue error.

I tried using a windows CD to boot, but it can't.

Please help.

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You should be able to fix this by reinstalling GRUB.

Boot from a linux live cd, open a terminal and type:

$ sudo update-grub

You should see something like (emphasis mine):

Generating grub.cfg ...
Found Windows 7 (loader) on /dev/sdaX

If you do not see a line containing Found Windows 7 do not continue. There is a different problem.

If you do see a line saying that windows 7 was found continue to the next step:

$ sudo grub-install /dev/sda

This will remove the windows bootloader (if there, I think you have already removed it) and replace it with the linux bootloader GRUB.

Now, restart your machine, you should be presented with a normal GRUB menu enabling to chose windows. If you want to completely remove GRUB search for a howto on restoring an MBR on windows.

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Check the links I think useful for you.

Help Ubuntu and Ask Ubuntu

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Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. – slhck Sep 22 '12 at 19:09

Sometimes you can use the linux live CD to boot from a system in this state. Reboot with the Live CD in the computer then when the boot menu comes up choose "Boot from first Hard disk"

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