Windows 7 - The wrong disk is marked as a system disk, causing complication.

Hello sevenforums.
I have a problem that i hope somebody here can help me fix.
one of my old disks that i want to remove is marked as the system disk even though my OS is not installed there and i need to mark my other disk as system disk.
i want to remove the old disk to make way for newer disks, but simply removing the disk causes boot errors, can anybody tell me how to mark my other disk as the system disk?

Do you have a Windows Recovery CD or USB ready ?
If yes then just remove the 'old disk.

In BIOS set disk you want to be the 'new' system disk as first disk (if more than one disk)
Boot recovery media. Run 'Automatic Repair'.
If repair reports errors that cannot be fixed, go to command promt and type:
bootsect /nt60 all /mbr

D: is the disk you want to keep and you don't want to boot through C:- correct?