NDSL turn on, gets a flicker then nothing

I got my NDSL at a garage sale a couple years ago, at the time everything worked, just missing some parts - namely the lower slot cover and the stylus. I found a site that i can replace the shell of the NDSL, i followed the instructions, but sadly the the touch screen tab for the cable got broke. i ordered a new motherboard to "replace" the bad/broken one. i followed the assembly instructions and i get a flash on the lower screen for a split second then it shuts off. i have tried to make sure all the cables are set tight, but i still have no luck in getting the whole unit working, any help on getting it up and running again will be grateful.