The Grub rescue prompt means that grub is not starting correctly.
To get Windows to boot again you need to re-install Grub or repair the Windows boot-loader.
Check whether your computer uses a BIOS or UEFI firmware. UEFI firmware may require different steps than I am posting here depending on the exact configuration.
To repair the Windows boot loader, you need a Windows Setup DVD for the correct version of Windows (7 or 8). If you don't have a Windows Setup DVD you should create one before you attempt to install Linux again. You can download Windows 7 Setup discs from the Digital River web site.
Official download links for Windows 7 SP1 ISO
Getting a Windows 8 disc is a little more difficult.
You do not need a CD key to repair the Windows boot-loader or boot configuration. You can also use the Home or Professional version to repair either the Home or Professional version. These disks are useful for repairing the Windows boot loader but you SHOULD NOT use them for installing or re-installing Windows. You must use the Windows disc and Windows CD key that came with your computer for installing or re-installing Windows. Also DO NOT repair Windows system files using these CDs.
Boot from the Windows Setup disc. When you see the Windows graphical Setup, press Shift + F10 to get a command prompt.
For a BIOS use this command to repair the Master Boot Record.
If Windows still does not boot, repair the partition boot sector.
Finally, if Windows still does not boot, repair the Boot Configuration Database.
If you have UEFI firmware instead of a BIOS you can use this command to repair the boot loader.
The above steps should allow you to make Windows boot again without Linux. After Windows boots again, create a Windows System Repair Disk before you attempt to install Linux. That will make it easier to repair Windows in the future.
Create Windows 7 Bootable Emergency Repair Disc - Windows 7 Recovery Tool
How to Create a "System Repair Disc" (CD/DVD) in Windows 8
To re-install Grub you will need a Linux boot disc or USB thumb drive. You will need the Grub files to be on the hard disk in the Linux root partition. If you installed Linux, the required Grub files are probably still there in the Linux root partition. You can install the Grub package or install Linux if the required Grub files are not present.
Boot from the Linux disc or thumb drive. Follow these steps to re-install Grub.
- Start a command shell
- Change to the root account
- Mount your Linux system partition on the hard disk
NOTE: Change "/dev/sda2" to the correct device name for your Linux partition.
mount /dev/sda2 /mysys
- Change the root to your Linux system
mount --bind /dev /mysys/dev
mount --bind /proc /mysys/proc
mount --bind /sys /mysys/sys
- Install GRUB
- Configure GRUB
grub-mkconfig -o /boot/grub/grub.cfg
- Exit from the root file-system shell
- Dismount everything
- Boot from your hard disk
- If the OS doesn't load repeat the above steps or repair the MBR to boot Windows
Grub will start first, and you will have to select the menu entry for Windows in order to boot Windows.