How to factory reset dead Apple iBook G3/366 (Firewire/Clamshell) to sell?

I have owned this Apple iBook G3/366 (Firewire/Clamshell) Special Edition Graphite M6411 since 1999-2000. Unfortunately, the computer has no power --- battery dead and YoYo power adapter doesn't work. I wanted to clean the hard drive before I sell it but I don't know if that's possible. Not that I can remember what's on it but I'd prefer to sell it clean.

Can anyone suggest or offer advice on what I should do? I tried all the troubleshooting ideas and none brought it back to life. Or is there a compatible third party inexpensive adapter that I could purchase that might power it back on? Thank you!