@krajiska: I'm not trying to discourage you - but it looks like your device is in a really weird and totally bricked state. All the tools that we know to usually work fail to bring it into fastboot mode.
You may want to check out the "simple debricking" thread for more information about u-boot, fastboot, and the entire machinery. For instance, you could try to upload eureka's hacked fastboot image which doesn't require the uboot bist - maybe that what is causing your problem. In any case, you
will have to read and learn
a lot of
extremely lowlevel stuff, including the layout and design of the chip.
Take a look at
this - I know it's for the Kindle Touch, but it probably applies to the K4 as well. Otherwise, look for "eureka", "fastboot", "imx_usb", and "bist", in the mentioned thread and in this forum. Good luck!