This simple tutorial shows you how to repair your Windows 7 boot loader (MBR) from Ubuntu dual boot or Ubuntu Live CD / USB. This can be useful if you don’t have a Windows CD or DVD on hand.

To do so, first boot into your Ubuntu system. When you’re in Ubuntu, press Ctrl+Alt+T on your keyboard to open terminal and follow below steps:

1.) First run below command to check your disk:

sudo fdisk -l

The output tells you the disk information:

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x016c8108

Device Boot Start End Blocks Id System
/dev/sda1 * 63 39054014 19526976 7 HPFS/NTFS/exFAT

2.) Now run commnad to install syslinux, which is a suite of lightweight IBM PC MBR bootloaders for starting up computers with the Linux kernel.

sudo apt-get update; sudo apt-get install syslinux

3.) Once installed, you can fix your Windows bootloader by running below command in terminal:

sudo dd if=/usr/lib/syslinux/mbr.bin of=/dev/sda

Replace the startup disk name /dev/sda in the above command according to the output in step 1.

Enjoy!