*Phew* blows dust off ole kindle keyboard. . . I have firmware 3.4.3 running on my K3. I don't know if you can download the latest firmware to your computer then sideload it to your kindle to get it running again. You might want to post in the Kindle Developers Corner about that otherwise you can get another cheap kindle 3 at shopgoodwill probably under ten dollars or less.
Amazon Kindle Model No. D00901
https://www.shopgoodwill.com/Item/80406799