Laptop won't boot; says "BOOTMGR is missing" after active partition was changed

The active partition is the partition which the system will use to boot from. In your case, you've changed it so that the required bootmgr could not be loaded. You need to set the partition named 'Reserved by system' to active. This partition usually has no letter assigned to it. You can set this with a bootable live USB running a partitioning program. Below I've placed a link which describes how to make such a live USB running easeUS:

http://www.partition-tool.com/resource/manage-partition/usb-partition-manager.htm

After you do this, everything should work again.

In the end I solved this by creating a bootable USB with the Windows ISO on it, and ran the "Repair" tool twice.

I essentially followed the instructions at: http://en.community.dell.com/support-forums/software-os/w/microsoft_os/3316.2-1-microsoft-windows-7-official-iso-download-links-digital-river.aspx

• In my case, I was using Windows 7 Professional (x86), so I downloaded that ISO.
• Then I used the "Microsoft USB/DVD download tool" to create the bootable USB.

Many thanks for the help.

In case that you only have windows, you have to boot from a cd. There is no other option, I have searched a lot for other options but they don't exist.

The only other option to solve problems on Windows is to press F8 by booting and opening a recovery console, but it won't work in your case.