You can fix the "Bootmgr is missing" error in Windows 7 using the Startup Repair option on your installation disc. If you have a computer with a preinstalled recovery option, use the Startup Repair feature from the boot screen.
- Run Startup Repair from Windows Recovery Environment
Insert your Windows installation disc, and restart your computer. Press any key when you see the message "Press any key to boot from CD or DVD." Select the language, time and keyboard options, and press Enter. Click Repair Your Computer, and select your Windows drive in the System Recovery Options box. Click Repair Your Computer, and select the operating system. Click Next, and select Startup Repair in the System Recovery Options box.
- Rebuild the boot configuration
Insert the Windows installation disc in the drive, and restart your computer. Press a key when the system prompts you to do so, and select the time, language and other options before pressing Next. Click Repair Your Computer, and select the operating system. Click Next. Click Command Prompt in the System Recovery Options dialog box. Type "Bootrec /RebuildBcd" without quotes, and press Enter.
- Use the preinstalled recovery option
Remove all discs from your computer, and restart it. Press F8 before the Windows logo appears, and view the Advanced Boot Options screen. Highlight the Repair Your Computer option. Select a keyboard layout, and press Next. Select your username and password, and click OK. Click Startup Repair in the System Recovery Options menu, and wait for Windows to complete the process.