you should really have done a guide from this site. Go to the 4.3 Guide, already linked and do it step by step.
PimpMyWii could have caused even much more trouble.
stick to the wiihacks guide
I am having the same problem. My system got updated to 4.3 and every card I put in says this card cannot be used. I can't even do a hack because it can't read the SD card. I have IJ game, white sandisk 2 gb card and it still cannot be read.