Something i didnt see in here, iv heard alot that if you run Dual boot with Windows (2 versions of Windows) you have to use the Windows boot loader, iv never ran a system with two versions of Windows because im not a sadist but anyway, from what iv heard Windows wants its own boot loader loaded, even though it shouldv worked, NOW so no one mistakes what iv said AGAIN i said iv heard that when you have more than one Windows on your PC with another OS, Windows wants its own boot loader.

Now, as for getting your HD back to just Windows, if you had anything on Linux back that up and then, back up EVERYTHING, take it from me iv lost things like 30 times because i was a moron with partitions, so back up everything including your stuf in Windows, then, you can use partition magic like you said, and delete all partitions and reformat, or you can just delete Linux, if you delete it first by accident without removing grub,
fdisk/mbr
has worked for me when i did that usually so you should be ok, just be sure your backed up.