Method 1:
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1. Put the Windows Server 2012 R2 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, a currency, and a keyboard or another input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type sfc /scannow, and then press ENTER.

Method 2:
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1. Put the Windows Server 2012 R2 installation disc in the disc drive, and then start the computer.
2. Press any key when the message indicating “Press any key to boot from CD or DVD …”. appears.
3. Select a language, time, currency, and a keyboard or another input method. Then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type Bootrec /RebuildBcd, and then press ENTER.

Method 3:
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1. Put the Windows Server 2012 R2 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, a currency, and a keyboard or another input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type BOOTREC /FIXMBR, and then press ENTER.
8. Type BOOTREC /FIXBOOT, and then press ENTER.
9. Type Drive:\boot\Bootsect.exe /NT60 All, and then press ENTER.

Note: In this command, Drive is the drive where the Windows Server 2012 R2 installation media is located.