First, at the health screen hold + and -, then push A a few time. If you are blessed, it will boot your wii into maintenace mode, then uninstall the bad wad. Unfortunately, that probably won't work.
When you hacked your wii, did you install ios60 patched with the trucha bug?
Or maybe you install Indiana Pwns?
If you did one of the two above, you can fix it with a modchip preconfigured to autoboot and a recovery disk. With out ios60 patched with trucha bug or Indiana Pwns installed, there is nothing you can do with a modchip.