1. How to Boot Your Infected Computer Using an USB Stick When BOOTMGR Is Missing Displays
If "BOOTMGR Is Missing" displays on you screen then I recommend that you watch this YouTube video which explains a solution that has allows users (it worked for me) to access all the files on my computer:
http://www.youtube.com/watch?v=dnRjxHKN6p4
In addition to your damaged computer you will also need another healthy computer to prepare the files needed on a USB stick with is used to boot up the damaged machine.
2. Rufus and Hiren's Boot CD
It involves using two programs called Rufus and Hiren's Boot CD. This method allowed me to access all of my Windows XP files (this same method can be used for more recent versions of Windows) by following the video and then booting with a USB plugged in
and using the Mini XP option to boot the machine.
3. Rufus
Download and install Rufus.
http://rufus.akeo.ie/
4. Hiren's Boot CD
Download Hiren's Boot CD 15.2
http://www.hirensbootcd.org/download/
Extract the .iso file using WinZip Evaluation version or similar software.
5. YouTube Video Procedure
Use the procedure in the Youtube video to use Rufus to put the Hiren's Boot CD .iso file on a USB stick
http://www.youtube.com/watch?v=dnRjxHKN6p4
6. Booting Infected Computer with USB Plugged In
Start up you computer with the USB connected and press F2 at first screen.
Change the boot order to that the USB sick is first in the list.
Restart the computer with the USB in.
The USB should kick in to action.
Select Mini XP (or similar for different operating systems) and it will hopefully load allowing all your files to be accessed and backed up.
7. Backing Up Files
Plug another USB into the infected computer and copy files across and save these files on another computer.
8. Scan For and Remove Infections Using Malwarebytes
This webpage show how viruses can be removed using Malwarebytes which is included in Hiren's Boot CD.
http://www.tech-recipes.com/rx/41669/remove-nearly-any-virus-using-hirens-bootcd/
Just follow steps 6 to 12.
This should help some people.
Regards
James Cox