I had to use boot-repair once on a dual-boot computer with Linux Mint and Windows 8 and it actually fixed the boot sequence so I could get back into my windows 8.

Boot-repair is a program to keep in mind!

Get boot-repair from Sourceforge.

Scenario 1:

You can still get into linux but not in Windows or anything else, install the program by copy/pasting these lines one per one in the terminal.

sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair

Scenario 2:

You can not get into any operating system. Download the iso file of boot-repair. Burn the iso on dvd or burn it on usb.

Try booting with it. You may need to change the BIOS booting order.