Same thing happened to my 5thGen Nano.
But guess what it wasn't the humidity.
IT WAS THE LACK OF HUMIDITY
The screen was just the way you described.
And I had been using it that way for about a month
THEN - I laid it on the edge of the tub one evening during my bath.
I forgot about it and retrieved it the next day.
There was a bit of moisture underneath, not inside.
AND THE SCREEN WORKED!
It's winter here, and humidity runs about 20%
After a while, the screen stopped working again.
So I simply blew gently my moist breath into the connector hole.
For about a minuite - and VOLIA! It works!
Who knew! You do now!