boot Windows from GRUB rescue

When GRUB is gone, so is the ability to boot into Windows. You would now need to boot from the Windows CD to restore the Master Boot Record (MBR). You can also use other boot CDs such as the Ultimate Boot CD for Windows, Bart PE or Hiren's Boot CD in case you don't have Windows installation media handy. Here are the steps:

• Boot from the Windows CD and choose "Repair". Alternatively, boot from one of the other aforementioned boot CDs and run a command prompt.

• For Windows 8 computers:

  1. Insert disc
  2. set boot order to disc at first priority
  3. reboot, wait for installer to load
  4. select language and keyboard type and click continue
  5. DO NOT CLICK INSTALL, instead click repair my computer in the bottom left corner
  6. click troubleshoot
  7. click advanced
  8. click command prompt and enter the commands below.
  

Add more tutorials for Operating Systems please.

• Run the the following two commands in a command prompt:

  bootrec /fixmbr
  bootrec /fixboot
  

As Gilles already pointed out, grub rescue only has a few commands which allow you to load modules (e.g. from a grub rescue disk).

In my case - booting from another source wasn't possible - the only option was to remove the hdd from the computer and use a cheap external hd case to connect the disk to another computer via USB. On that computer, I used MbrFix to fix the mbr.