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.
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
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.