Freezing up at Black Health Screen
When I boot on my Wii, it loads as far as the black "Press A to continue" screen warning about seizures and epilepsy or what have you, then... stops. In fact, the option to press A never shows up and I am unable to connect the Wiimotes.
This particular Wii is not modded though I have soft modded two previous Wiis with no problem.
The only suggestion I seem to have found is to boot up a disc of New Super Mario Bros Wii, as that contains the 4.2 update and this error sometimes occurs if an update is corrupted. However, I don't have a hard copy of the game handy.
EDIT: Tried booting into NSMB after leaving it unplugged for an hour but no dice. Also, the Wiimotes now connect for some reason, but it seems to be unrelated to the game.
The resource files of the system menu (stored in NAND flash) are corrupted; there is no way for you to repair it yourself. If the system is still under warranty, you are best off sending it back to Nintendo. Otherwise, you can replace the main board.
Ports: GameCube Controllers, GameCube Memory Cards, Sensor Bar, SD Slot, USB Ports, Power In, A/V Out — Currently out of stock.
I had the exact same problem where the initial health warning screen loaded with the flashing click A button to continue type message. After pressing the A button a black screen would just hang and the system menu would not load.
The following steps fixed my problem:
1: Unplugged the PSU, RCA, and sensor bar cables from the Wii.
2: Unplugged the PSU from the wall.
3: Removed SD card, Gamecube memory cards, and Gamecube controllers from Wii.
4: Let everything sit in this state over night.
5: Plugged PSU into wall socket
6: Plugged RCA cable into Wii
7: Plugged PSU into Wii
8: Powered up the Wii with the Wiimote power button (not the power button on Wii)
This resulted in the Wii booting to the system menu screen. I then plugged the sensor bar in and the SD card. Wii is currently still working.
Following the steps above, if I tried to boot the Wii using the power button in the Wii, the problem persisted. I was only able to boot to the system menu using the power button on the Wiimote.
Maybe this will work for others with this issue.