Well in that case, there is no easy fix. Seeing as you presumably don't have BootMii/boot2 on this Wii, you can't use that to fix it. I assume that seeing as you didn't install BootMii/boot2, it wasn't possible to install it, and therefore the hardware method for installing BootMii/boot2 will not work. Unless you happen to have a NAND backup from BootMii/IOS, there may very well be no way to fix the Wii. The problem is you must have a Korean Wii, with it's region changed to US or EU or whatever. This causes Error 003 on 4.3 (and possibly 4.2, can't remember). The "solution" devised by some people in the Wii scene is to install an old IOS (IOS60) in place of IOS80. You must have reinstalled IOS80, but installed the proper IOS80 instead of IOS60 in the IOS80 slot. Therefore Error 003 shows.
The only ways I know of to fix this are:
(i) restore NAND dump with BootMii/boot2 (simplest, but only works on older Wiis were BootMii/boot2 can be installed)
(ii) use BootMii/boot2 to load HBC, then load a homebrew app and either install IOS60 to the IOS80 slot, or else install System Menu 4.1 and IOS60 to the IOS60 slot (still fairly straight forward)
(iii) use Priiloader to load HBC, then as (ii) (requires Priiloader to already be installed before brick, and slightly more risky than with BootMii/boot2)
(iv) use the recovery menu and an autoboot disc to load a piece of homebrew to fix the issue (requires a modchip and patched System Menu IOS, or very patched System Menu IOS ["cIOScorp" or "darkcorp"]; alternatively you can use a modchip that supports autobooting retail discs along with a copy of Super Smash Bros Brawl and the Smash Stack exploit; there is also another lengthy workaround for using other game based exploits as well, modchip still required)
(v) use a hardware NAND reprogrammer to flash a backup made with BootMii/IOS (requires specialist hardware, which may not be available anymore, and a certain level of expertise; alternatively you can pay someone else to do it - you MUST have a BootMii/IOS NAND backup for this to work)
Without BootMii/boot2 or Priiloader, it depends whether the IOS80 you installed had any patches. Even if it did, you most likely need a modchip to be able to use option (iv). Option (v) is probably a last resort, and will ONLY work if you installed BootMii/IOS and made a NAND backup before bricking the Wii.
I can't think of anything more to tell you.