Nintendo's customer support page has a database for error numbers. It appears that 003 has its own page, though, asking you to call customer support directly. You might have quite the fun repair on your hands. After calling NIntendo, you might want to take a look at our selection of Nintendo Wii parts. Let us know what they tell you!
This happens when you install a US/Europe/Japan Wii Menu on a Korean Wii, or add the Korean common key to a console with a U/E/J Wii Menu. Information on fixing can be found at https://wiibrew.org/wiki/Error_003
Sounds like you accidentally bought a hacked Wii. When you 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 you out of it. If nothing happens then you may be out of luck. Since you bought from Korea and it still allows you to play it in America then there is a good chance that your Wii is modded. I would say return it to the person you got it from but that seems to be out of the question.
