Welcome to the forum. There is a known issue causing that at the moment that NOW TV are looking into fixing, although I don't know when.
However you also mention that you suffer from buffering as well so it could also be caused by a poor Internet connection. Try rebooting your broadband router to make sure it's selected the best wifi channel for your home. You could also experiment with moving the box a little, eg bringing it into the open or away from other electrical appliances or crowded shelves to see if that gives you any improvement.
@Kell81 I did experience the 'no content' issue once, but it turned out it was a wifi issue in my case and rebooting my router fixed it.
There are on-going reports of the 'no content' issue for some box users though, so if your box is otherwise fine but you've had the 'no content' issue for a while it's likely you're suffering from the bug. No idea why it affects some box owners and not others and probably not much you can do about it until NOW TV get to the bottom of it.
If you are still suffering the picture problem though that's likely a separate issue, might be worth having a word with live chat and doing a bit of troubleshooting if you haven't already. You can get to live chat from the Contact Us page
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ive been having the no content on half my film genres for about three months, i dont know why im still paying for it because now im getting nearly all the genres showing no content and some of my enterrtainment, ive contacted now tv they say after a hard reset soft reset, checking my internet and even buying a internet wifi booster that it is a technical fault they are dealing with but, they have done nothing,fraid to say unless something sorted i am ending my contract and going elsewhere., three months to sort a technical issue is madness...