How to boot without bootmgr

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.