To fix BOOTMGR without a CD, you need to access Windows Recovery Environment (WinRE) using this method – boot your PC, and when the Windows logo appears, press and hold the power button until your PC powers off. Power on your PC and repeat the previous step. Do this three times and you should boot into WinRE. Once you’re in the Windows Recovery Environment (WinRE), use one of the following methods to fix the BOOTMGR:
Click on Troubleshoot > Advanced > System Restore and follow the steps in the wizard.
Again, go to Troubleshoot > Advanced. Click on Startup Repair.
Open the Command Prompt using Troubleshoot > Advanced > Command Prompt. Type these commands and press Enter after each one:
bootrec /fixmbr
bootrec /fixboot
bootrec /rebuildbcd
sfc /scannow