This is about the 7th case I have heard of (exact same situation as you) that GX has bricked a wii. The 3rd one I read about made me never use GX again.
Unfortunate. Cfg and Wiiflow are a much more reliable choice....so many people are dead set on using GX.
Anyway....Did you install bootmii as boot2? OR...do you have a nand backup (nand.bin and keys.bin) ? How old is your wii?
What revision of GX are you using and what is your HDD formatted to ? (curiosity)