Normal format checks over errors and tries to mark bad sectors and such, and sometimes stops if too many are found. Unconditional format disregards any bad sectors that are found and just tries to keep pushing on.
Looks like your drive might have hardware trouble or physical damage, IE bad sectors. And if no one's told you, you can't repair bad sectors. If you ever get it formatted, do a surface scan with Scandisk, and if bad sectors come up, the drive's crashed and gone farming (reference to when the drive heads start plowing little throughs on the surface). Or, while formatting, if you see messages about trying to recover allocation units, the same thing applies.