that doesn't sound like you are actually following a fully supported wiihacks guide to softmod your wii, or using approved techniques to go further on specific problems.
can you run games?
black screens on apps can be fixed but it would be easier for you to just stick to a softmod guide in the recommended section to get you up and running.
I can recommend the softmod any wii guide which is linked below.
if you can specifically state what guide you used, when you did the update (after that, safe updater doesn't mean it will not stub your cios..) and what the actions were you took before problem arouse, we can help you here, but again it would be easier to stick to a guide to hook you up.
As you are on 4.2 you can bannerbomb hackmii installer (there are different versions, one should work), and install a whole bunch of wads (some are already patched etc. so you don't need to take care of it) to hook you up