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I installed windows 7 64-bit, I then installed Ubuntu 10.10 which went successful. I then reboot and to my surprise i didn't even see the options to select the OS to boot from.

I logged in to Ubuntu 10.10 and went to my computer, I can't see my windows partitions.

How do i get back my windows OS?

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1  
reboot your computer and hold the shift key to load your grub , think that should fix your problem –  Alagiboy Mar 2 '11 at 22:36
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Are you sure you installed Ubuntu onto another partition? If you installed Ubuntu on the same partition your windows may be lost. This may be a stupid question like: "Make sure your power cable is connected?". But i just want to be sure g What is the size of your Ubuntu partition? And is there free space or the windows partition when gparted is invoked? –  Darokthar Mar 2 '11 at 22:46

2 Answers 2

Grub should automatically display itself if it detects more than one OS. Since it didn't display, I'm guessing you need to update the grub config file. This is assuming you're using the default of grub2 (or grub-pc).

Open a terminal in linux and type:

sudo update-grub

It should print out some information about the OS's it finds, including win7, and automagically update the config file. On reboot, grub should automatically appear with an option for win7.

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Run the following from a terminal in Ubuntu, assuming you have sudo privileges and "/dev/sda" is the device file for your hard drive.

sudo fdisk -l /dev/sda

Here's an example from my system.

Device Boot      Start         End      Blocks           Id       System
/dev/sda1         1               19440   156150000+  7      HPFS/NTFS
/dev/sda2         19440        19683   1953125+     82    Linux swap / Solaris
/dev/sda3         19683        19696   99968+         83    Linux
/dev/sda4         19696        38914   154368098    5      Extended
/dev/sda5         19696        22127   19531219      83    Linux
/dev/sda6         22127        38914   134836816    83    Linux

Here, "/dev/sda1" is marked "HPFS/NTFS". This is my Windows partition. If your Windows partition did not get deleted or formatted into a different file system, you'll also see one like this.

Typically, new computers come with one large windows partition that takes up the whole drive, optionally with a rescue partition. Hopefully you have a Windows 7 CD/DVD in case you need to recover the Windows MBR. Anyway, in order to install a new OS on such a system, you have to make room - either by deleting/formatting the existing Windows partition or resizing it. Hopefully you resized your Windows partition to make room for Ubuntu.

If your Windows partition survived, the problem becomes one of reconfiguring grub. Hopefully the following documents are helpful.

Arch Linux Wiki - GRUB - Dual booting with Windows

GrubHowto

Here's my GRUB entry for Windows XP that Ubuntu added automatically

# This entry is automatically added by the Debian installer
# for a non-linux OS on /dev/sda1
title Microsoft Windows XP Professional
root (hd0,0)
chainloader +1

Leave a comment on results. I'll edit this answer with more details if you have trouble.

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