I could not be able to see my D: , E: and F: drives on windows explorer.why?

I created a partition as primary for the USB drive in order to make it bootable. First I select a disk named disk 2. Secondly, I created a partition as primary on the disk. Third I clean the disk. Fourth I format the disk using fat32. Then I select the partition 1. lastly I type the command active and type command assign letter=z to assign the letter z to the activated partition.Then I copied windows 7 onto it. I faced two problems. I could not be able to boot from the usb drive. Secondly my other drives d:, e:, f: which have a lot of stuff, disappeared from the explorer screen. I am very much frustrated. Can u please help me guys?