Can't Dualboot with Windows

[h4Ck3D001]

Hi,
So when I try to dualboot, first, Windows won't show in GRUB, and second, when I add it to Grub Menu, I just get an Error that says something like: "No Bootable System found, press Ctrl + Alt + Del for restart."

Am I doing something wrong?

If you already made a Dualboot with Windows and Zen Installer/Arch, I would be very happy if you could show me how to do it! (I have one hard drive.)