Is the phone getting Now OK through the same WiFi as the laptop and stick, or on your 3/4/5G?
If the latter, try the phone on your WiFi, and report back.
If the phone works on 3/4/5G, but not on WiFi, this would point to a problem with your broadband.
Is everything else fine over your WiFi?
Who is your ISP?
If it is Now, then go into Broadband Buddy and tell it you are an adult.
Have you tried to restore the NOW stick back to factory settings?
When you say that you click on a programme you want to watch then the screen goes black on your NOW Stick or PC, is it for a split second and do you see a spinning circle for about two or three seconds ?
If so, then this is how the NOW content starts up on my devices such has my Youview box, NOW box etc.
Don't use a smartphone or tablet to watch NOW so don't know if the start up or swapping live NOW channels works differently.
Should it be that the screen goes black for longer and no sign of the blue spinning circle, then out of curiosity are you also using your PC with the television via a HDMI port or are you using the inbuilt screen on the laptop ?
if both devices are connected directly to the television via HDMI, then would you have another television to temporary test out ?
Edit - Just read your heading saying " Unable to Watch Anything ", so ignore my first couple of paragraphs, though i would be tempted to try another television with your Stick, plus if you have mobile data, temporary test the Stick using your smartphone has a wifi hotspot.