How do I determine my top screen isn’t working?

I believe that the top screen of my DS Lite is broken. I power the device on, the bottom screen flashes, then it turns off. I disassembled the DS Lite and checked the top screen ribbon cable. It doesn’t look bad, maybe one tiny minuscule nick, and a bit of gunk. But I don’t think that’s enough proof to determine it’s broken. How do I make sure this is the case? Also, how much damage does a ribbon cable need before it’s considered “damaged?”

Also, also, there’s some writing on the top screen and motherboard from the previous person that owned the device, and I don’t know what it means.