Sounds like آپ accidentally bought a hacked Wii. When آپ upgrade the firmware found the hack and now your Wii may be bricked. Try this: while holding down the reset button, turn on the power to the Wii. If a menu comes up then your wii is definitely hacked but it has a brick safety program to get آپ out of it. If nothing happens then آپ may be out of luck. Since آپ bought it from someone and it still allows آپ to play it then there is a good chance that your Wii is modded. I would say return it to the person یا store آپ got it from but that seems to be out of the question.
