you are all confusing bootmgr with MBR(master boot record) the MBR is used by the HDD to allocate files the bootmgr is the win7 kernal launcher. if you format the disk with the operating system the MBR will give you the error of no bootmgr because you deleted it. you nee to install an OS back on the drive.
Really, all? Read my first line: "If you fully formatted the entire disk and removed the OEM partition that has the install files you will need a Windows installation disk."