type 'control userpasswords2', no quotes
Put a check on 'users must enter...' and restart computer.
2)windows key+pause break key, advanced>settings for startup and recovery, click 'edit'. make sure you delete the 'multi(#)...' line that you don't need and save the file. But, if you're sure the other install is in a DIFFERENT partition (which I don't think is the case), you can just erase/reformat that other partition.