My brother wound up updating his DSi to 1.4.1U. Trying to fix it, I tried to flash and the light did not light up. I tried putting it in both way (arrow toward the front, arrow toward the back).
might be a broken led light, might be a busted wire, if all else fails then you can use a copper wire into an outlet just make sure you wear some rubber gloves or you'll die from electrocution lol
For me if you want to emulate the DS the best option is on Android, use DraStic and a controller that holds your phone... it's clunky but it works insanely well. The next best option in my opinion is using a New 3DS XL, not really emulation but hacked it works really well.