i don't really think it's overheating, because he's saying the system freezes sometimes right when he turns it on.
sounds like your system might be corrupted. you could try going into maintenance mode on your wii. i think you hold down the plus and minus buttons at the first screen that pops up when you turn on your wii (the warning screen). from there, you could try a couple different things. updating your system again might help. if not, you might have to reformat your system. if you want to do that, back up all the game saves you can, because reformatting the system will delete everything (and i mean EVERYTHING!).
i'd say hold off on reformatting until your tried everything else.
come try out the computer game i've been working on for my high school senior project, titled sling ball. http://vgchartz.com/forum/thread.php?id=76669&page=1
you can view a few screenshots from the game in my photo album here; http://www.vgchartz.com/photos/album.php?album=2312
yes, this is vonboy's alt account. i can't log into my original account, and i'm not sure if i will ever be able to.
Proud Member of the Official Yoshi Fan Club!.
