After re-installed Ubuntu 12.10, I found my windows cannot boot from GRUB boot loader. So I have to do the following to resolve this issue (I assume you installed GRUB boot loader in the same place you install Ubuntu, otherwise you will be able to boot windows but not Ubuntu.):
- Install Boot-Repair in Ubuntu 12.10.
- Open Boot-Repair and go to Advanced options, select “Restore MBR” and hit apply. Reboot.
- Now you should see your original windows boot screen. But now you cannot boot Ubuntu anymore. So we have to make Ubuntu boot again. Install EasyBCD which is free for non-commercial users in windows. Open it and go to “Add New Entry” -> “Linux/BSD” -> type “GRUB2” -> give it a name -> click “Add Entry”. Don’t be fool by the text “Devices: (Automatically configured)”! You have not finished yet.
- Go to “Advanced Settings” -> select Ubuntu OS -> in “Basic” tab, select the drive where you installed Ubuntu -> save settings.
- Reboot. Done. Both windows and Ubuntu boot should work now!