Try looking in priiloader under the settings there's one there called use ios it should be set to use system menu ios. if all else fails use the sticky guide to update to 4.2 and cross your fingers.
I had this problem and it turned out I had priiloader loading ios 249 to boot discs from the...
That's what it looks like you have stubbed the system menu ios for 4.2 and below and putting 4.3 ios 80 on but did you install the 4.3 system menu?
Did you have priiloader and does it still work (hold the reset button when booting)
If your still looking for the online method go into priiloader then settings next to the bottom is (show beta updates) turn it to on.
Then go back To main screen of priloader and click on update.
Just take the bootmii files off your sd and put them on your computer for safe keeping.
In priiloader goto settings and set autoboot to installed file not systems menu that will launch USB loadergx on
Boot if you got the forwarder installed.
Sounds like your boot up problem is preloader go to the settings at the bottom then change autoboot to system menu.
As for the update you could also read the sticky hack any wii 4.3 and below on the main hacking page.
Waninkoko was going to use ios58 as a base with rev 20 but then said he wasn't going to use it just Before release maybe in future revs it will be included.
Is priiloader set to boot the system Menu ios also you could try and install ios 70 and the system menu again.
Have you tried to boot without anything plugged in.
Try running dop-mii and run a system check to see that your ios's are ok maybe it had cios Corp installed at somepoint and the ios's ain't in good order.