HD zero-overwritten

[snip]
Recently, I bought a latter-day half-computer which only has an USB input which he used for Knoppix 7.4.2.
While trying to find the elusive "any" key on the keyboard, I [snip] managed to overwrite the entire HDD with zeros!
Now what!!??
$ sudo lshw -short
and
$ sudo fdisk -l
do find and correctly describe the HDD; but it (the HDD) remains zero-overwritten and resists all and any attempts to touch it.
QUESTION: can knoppix - run from the USB - somehow format the said HDD? Any formatting while FAT32 would e the best...

Have you already tried gparted from the menu?
If you overwrote the whole HDD it could be necessary to create a new MBR or GPT.