How to securely erase damaged hard drive
Solution 1:
I'd recommend DBAN (https://dban.org/). It's free. You can load it to a flash drive and boot from that (https://www.lifewire.com/how-to-erase-a-hard-drive-using-dban-2619148), or burn it to a cd if your BIOS are too old. It has a few different options from a quick erase to a 35 pass overwrite.
After that I'd recommend something like what Greg said, perhaps a sledgehammer?