How to Wipe a hard drive

  1) for that you can use Hiren boot cd
           or
       get parted magic and use Unetbootin to make a bootable USB drive

  2 ) The system should booted with parted magic

  3) Determine which drive is the one you want to wipe. The tools on the desktop should show you pretty obviously what drive /dev/sdX, most likely it will be /dev/sda

 4) open terminal type
       hdparm -I /dev/sdX
     This will show the information pertaining to this drive

  5) If the drive shows that it is frozen (no “not” to frozen) you will need to unfreeze it. The most effective way to do this appears to be to put the computer to sleep. To do this:
         a) type

echo -n mem > /sys/power/state

b) This will put the computer to sleep. Once it’s asleep, you should be able to wake the computer up (touch some keys, move the mouse…)

6) Run the informational hdparm command again:

hdparm -I /dev/sdX

  Ideally it will now show “not frozen”. If the drive still shows frozen, ensure that you don’t have any sort of bios password locking on the drive, and then the next best option is probably to move the drive into a different computer.

7)Now set a password so we can continue (here password for example "Pass")

 hdparm --user-master u --security-set-pass pass /dev/sdX

8) We can again run the informational hdparm command.

 hdparm -I /dev/sdX

 Now we should see “enabled” in the security section. Bingo. We also see the estimated time to wipe the drive.

9) Let’s wipe this drive. We can time the command if we’d like information about how long it actually takes:

time hdparm --user-master u --security-erase pass /dev/sdX

10) Relax. Go do something else for awhile. 

We can see that my drive ended up taking 299 minutes.

more information here