Googled this up, see if you can borrow another DSi or a DS:http://gbatemp.net/t253134-dstti-1-4-1-u-j-fix-for-dsi
Of course, I don't actually know if it'll work, but this is probably a good start
Your NDSi is not working because NDSis are crap. Get a DS Lite, or, even better, wait for the 3DS.
Thank you for the intelligent, constructive, helpful, useful, meaningful response.