I assume you want to format the drive anyway later on, then
Remove all your Harddisks from Computer. Connect the locked drive. Boot from CD a Live Linux http://knopper.net/knoppix-mirrors/index-en.html
and apply on console
dd if=/dev/null of=/dev/sda
Do NOT try these examples; they will cause data loss! The following examples are provided to warn about the dangers of dd, if used incorrectly. Trying any of these commands with the proper privileges will almost certainly result in major data loss, and may make the system unusable. In order to prevent accidental copying and pasting, "dd" has been replaced with "[dd]" here.
This overwrites the complete first hard disk
with null bytes, erasing it (though not in a manner that is as secure
as overwriting with random data):