Black Screen of the iPod nano touch

Try the original screen (if it was cracked, but the picture was working). If it is still dark, you have likely blown the fuse on the board, or a filter. I am not familiar with this model in particular, but you would need to get a schematic and board view if thats the case, find the backlight fuse, check continuity and replace it if power is not flowing through it. This will be soldered on the board though, so if you have no experience, it is best to take it to a repair centre.