As a user of Now Tv I also had problems with my Now box.
I got hold of a 100% new box and updated it, reinstalled apps,passwords etc.
To the best of my knowledge Now TV has given no explanation for the loss of service yesterday and could not even APOLOGISE in their two sentence service updates.
Even now I am not convinced that everything is OK. If i go into settings,system, about, where it shows "Now TV Account" at the top underneath where it should show the username, mine says "Not Available" !
It would be nice now that the long Bank Holiday Weekend is out the way that we got some official say on what the issue was yesterday (I hadn't even noticed that there was a two-sentence service update) rather than leaving it for us to guess.
With my Now TV Stick I also get that 'Not Available' thing..... and I also notice when I hit the Star Option Button on the Now TV App I don't get the option to delete or move App (I'm assuming those options should be available????) as I would like to move my Now TV App from App position 13/13 back to the top (just a little thing). So yes, are things totally back to normal, but at least we can watch things again!!!!!
Before I used my new black box I had the same issue as you. Reinstalling the Now tv app added it to the end of the list. Normally it would appear first in the apps list and even "normally" it does not have the function to delete or move the app, as Now tv wants it to appear first !
In your case I would try a hard reset to revert to factory settings which should make the Now app appear at the top of the list ,the only downside is you would have to reinstall all your other apps as well.