Why does 0000FE00 appear when I turn on my DS?

Couple of fixes are available if you do a Google search with error code 0000fe000:

" Start your DSi and wait until the Battery is empty. (Having an empty Battery lowers the time to boot up . The Ds got two internal flash memorys that are both damaged when you have this error. With the low Battery the resetted one gets loaded while the other can't in the same speed)

Remove the Bolts and extract the Battery for around 1.5 hours.Why we did this? All the Electricity needs to be out of the System to make sure it's only getting the Bootup Information from the Chip that got resetted and not from the other, if the other one could send it's information, we would still have the Error.

Reinstall your Battery.

You need to be fast now: Insert your Flashcard, and start your DSi.Start the Application you used the last time, before the Error appeared and close it legitly. In case off the SuperCard DSTWO SNES Emulator, just press the Exit Button. Other Flashcards like the R4i need to be soft resetted to the flashcard's menu, and need to boot up some game's rom.

-Not Necessary but just feels a little more safe- Format your NDSi.

Charge your Battery and enjoy playing your NDSi Systems again."

As well as "Some users have been able to solve this problem by resetting the system. To do so, hold down every button while the system is on except the D-Pad and power buttons. "

From here and here as well. Hope this helps, good luck