Windows 7 bootmgr is missing-- Resolved Using WinRE

Perform the following methods to resolve the issue:  Method 1: Startup Repair from the Windows Recovery Environment (WinRE)
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1. Insert the Windows 7 installation disc into the disc drive, and then start the computer.
2. Press a key when the message indicating "Press any key to boot from CD or DVD …". appears.
3. Select a language, a time and currency, and a keyboard or input method, and then click Next. 
4. Click Repair your computer.
5. In the System Recovery Options dialog box, choose the drive of your Windows installation and click Next.
6. At the System Recovery Options Dialog Box, click on Repair your computer.
7. Click the operating system that you want to repair, and then click Next.
8. In the System Recovery Options dialog box, click Startup Repair.

Refer the following link for more information:
http://windows.microsoft.com/en-US/windows7/What-are-the-system-recovery-options-in-Windows-7
To know more about “Startup Repair” visit the following link:
http://windows.microsoft.com/en-us/windows7/Startup-Repair-frequently-asked-questions

Method 2: Rebuild BCD using the Bootrec.exe tool
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To run the Bootrec.exe tool, you must start Windows RE. To do this, follow these steps:
1. Put the Windows Vista or Windows 7 installation disc in the disc drive, and then start the computer.

2. Press a key when you are prompted. Select a language, a time, a currency, a keyboard or an input method, and then click Next.

3. Click Repair your computer.

4. Click the operating system that you want to repair, and then click Next.

5. In the System Recovery Options dialog box, click Command Prompt.

6. Type Bootrec.exe, and then press ENTER.


Refer the following link for more information:
How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows

http://support.microsoft.com/kb/927392

Method 3: Use the Windows Recovery Environment (WinRE) to run System Restore
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1. Insert the Windows 7 installation disc into the disc drive, and then start the computer.
2. Press a key when the message indicating "Press any key to boot from CD or DVD …". appears.
3. Select a language, a time and currency, and a keyboard or input method, and then click Next.
4. Click Repair your computer.
5. In the System Recovery Options dialog box, choose the drive of your Windows installation and click Next 
6. At the System Recovery Options Dialog Box, click on System Restore.
7. Follow the System Restore Wizard instruction as usual and choose the appropriate restore point.
8. Click Finish to restore the system.

To know more about “System Restore” visit the following link:
http://windows.microsoft.com/en-us/windows7/System-Restore-frequently-asked-questions
If the above methods do not help, you may try to follow the methods mentioned in this article:
Error message when you start Windows Vista: "The Windows Boot Configuration Data file is missing required information"
http://support.microsoft.com/kb/927391
Note: This article also applies to Windows 7 Operating system as well.

http://answers.microsoft.com/en-us/windows/forum/windows_7-system/windows-7-bootmgr-is-missing-resolved-using-winre/8bb148bc-8035-4847-9696-888f7a0a9720