Hi,
Not sure but the usual thing to check:
Does the pin you're trying to use have other functions mutliplexed to it, like ADC, Comparator, USB etc and does any of these peripherals need to be turned off for the pin to work in the mode you want. I see you've got the comparator covered but how about the ADC?

What do you mean by there is no display? Do you mean it doesn't the display the result or do you mean it doesn't display anything?

Again, check each pin against the datasheet, does have anything that may need to be turned off?

/Henrik.