Hello Jimmybeam, welcome to Vista Forums! Be Advised
: doing this WILL
remove all the date on whatever drive (HDD) you do it to.
Boot into Safe Mode
then choose the command prompt option, once in the command window type these commands ...
diskpart <enter> after each command
selcect disk # (of the HDD you want to format, it can be found in disk management)
clean all <enter>
The last time I did this to a 500GB HDD it took over 2 hours to complete; this writes zeroes to the entire HDD and all the data will be un-recoverable once it completes.
If I wanted to do "disk 0" this is what it should look like, then hit enter, the second snip is what you get when it finishes.
click this inage to enlarge