How to fix the MBR for Windows 7?
Solution 1:
Try EasyBCD. EasyBCD is an advanced GUI application that makes it easy to modify the Windows bootloader and the entries in it.
Choose BCD Deployment, and write the MBR.
Solution 2:
I have solved this with a Boot-Repair disk (I put it on a USB flash-pen, but one can burn it on a disk if necessary). I had used the program mainly to repair the grub in linux, but it has an option to repair the MBR.
So, boot into the Boot Repair disk/usb, and check "Restore MBR" (instead of "Reinstall GRUB").
It works fine, the normal boot in Win7 is back in place.
Solution 3:
Check here: grub says unknown file system. what do I do?
Follow this: https://help.ubuntu.com/community/Boot-Repair