I would give it about 10 to 15 minutes if it is stuck on the NowTV pink welcome screen, then if it was me i would try a full factory reset by holding the small reset button on the stick for about 6 seconds.
This is a bit of a long shot and i am not sure it will work whilst stuck on the NowTV pink welcome logo screen.
Is to see if you can access the factory reset option via the secret hidden menu on the stick.
To access this hidden menu press home button 5 times, quickly followed by pressing the FF button 3 times, quickly followed by pressing the RW button 2 times on the NowTV remote.
Have you got another TV just to temporary test the stick ?
If so, i would hook up the stick to a different TV using the supplied power adapter, reboot your router and try another factory reset, this time maybe hold the reset button for about 12 secs whilst the stick is powered up to see if the same thing happens.
Other than that, unless somebody has come across this problem with a known fix, then maybe look at getting a replacement stick under warranty.