to lock C: drive the DWORD value would be 10bin(2dec) not 11011111111111111111111111111111bin. Following values lock the drive typed at right side. (1a : 1 locks A: drive, and 12cd: 12dec(1100bin) locks C: and D: drives. 1a 2b 3ab 4c 5ac 6bc 7abc 8d 9ad 10bd 11abd 12cd . . 16e . 32f . 64g