BOOTMGR Missing

If its a windows 7 or Vista machine, see if it gives you an option to run startup repair, it may take care of for you. Also many manufacturers put a recovery partition on the hard drives, you might Google for your model to see how to access it, doing that may at least let you get to factory settings.

put installation media for the version of windows you have onto a flash drive and boot it, then fix the bootmgr issue as if you had a cd drive. Best of luck!