how to format the HDD to low level format

Low level format via LiveCD Linux

Assuming you mean zeroing the hard drive as being the same as a low level format – from a live cd

sudo dd if=/dev/zero of=/dev/sdx

replacing the x with the drive letter of your drive (likely /dev/sda if you only have one hard drive) – be warned, on a 500gb hard drive, this could take some time. You could also use dcfldd which uses the same basic syntax as dd commands, but is about twice as quick. If you want to use dcfldd,

sudo apt-get install dcfldd

after you have enabled repositories. In which case the syntax would be

sudo dcfldd if=/dev/zero of=/dev/sdx

again replacing the x with the appropriate drive letter.
You could also use darik’s ‘boot and nuke’ live cd and it will essentially do the same thing.