Your first trouble sound like they would have been fixable. A failed system menu update due to power loss can be very bad. 4.2 kills bootmii, so no surprise it does not work. Sorry to say, but I feel this will be a full brick, only fixable by a nand flash with an infectus chip.
Read- OH SH*T: Black Screen of WII!!!
Test all of your options. Let me know what you find.