okay from what i understand, xbox uses drives x, y, and z as cache drives.. these are important drives for the xbox.. the xbox uses this as temp space for games so loading times do not take as long.. this enables games to load faster as to reading them off the disk everytime a file is needed.. so you should have left drives x, y, and z alone.. that was your first mistake.. also, im hoping you kept your dive E.. the xbox uses drive E mostly game saves and other requirements.. drive D is just the xbox dvd drive.. and well im assuming you know what drive c is for.. well since it sounds like you just reformatted the drive and removed some of the xbox's important files.. so you will have to reformat using SlaYers 2.6 or something like that so that you will have the original xbox dashboard and files back in working condition.. sorry i can not tell you where to get SlaYers 2.6 but you can try searching on google for it.. but in anycase, without drive x, y, & z you wont be able to any games on the xbox..
if you have any more questions, just ask and ill try to help you the best i can..