by lock...do you mean make it unaccessible? or hide it...as can't see it to open it or use it?

You can hide any of drive with registry editing. But then you would need to re-edit the registry each time that you needed to use the drive!

goto start>run

Type regedit and press enter. This will bring you to the registry editor.To hide any drive you have to follow these 2 steps

STEP1: Hidding Drive
goto HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\Explorer now create a new DWORD value NoDrives and set its value as

2^(Alpha Number of Drive Letter-1)
where Alpha number are simple counting of alphabets from A to Z as 1 - 26

for example: to hide C drive
Alpha number of C is 3 so 2^(3-1) = 4 (decimal value)

If you want to hide more than one drive than calculate the value of each drive as explained and then set sum of those numbers as value

Step2: Prevent Access to the drive
Now as we have make our drive invisbble but it is still accesible so to lock the drive we will create another DWORD value at

HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\Explorer
create a new DWORD value NoViewOnDrive and set its value same as you have calculated for hidding the drive(s)

Now your drive is locked. If you want to unlock and unhidden the drive then just delete these two keys and your drive is again accessible. You can also create two .reg files one for hidding and locking and another one for unlocking and unhidding.