***UPDATE***
Firstly, thank you everyone for all the suggestions!
So, as it happens my son has 2 fire tablets, as he is autistic and loves to turn the brightness all the way up so the charge doesn't last very long, so we purchased a second so we can swap them out when one needs charging! Anyway one of them got water damaged last week, but it was under warranty so we were able to return it and they sent us a brand new replacement, which came today! And as it turns out the new one connected just fine!.
Soooo I'm going to do a factory reset on the old one, and see what happens, but if the problem persists I'll start firing through some of the fixes you all kindly suggested!
