@Jackie: You can find it here:
http://pastebin.com/Wdw4L7yT , look for mmcblk0p2-4.0.0 image and for diags_kernel-4.0.0 image.
See
https://wiki.mobileread.com/wiki/K4_Index#De-Bricking for how to reflash the partition & kernel.
You can achieve the same thing and more from within the main mode by jailbreaking and installing the USBNetwork hack. Much easier for a non-geek than reflashing IMHO.