Hi @Anonymous User
If it's a six digit code showing on the television screen when you first setup and activate the NOW Stick, then it sounds to me the Stick is for some reason factory resetting itself.
The only thing i can suggest is to hold the reset button on the Stick for about 15 seconds whilst powered on and setup the Stick once again (make sure when asked you use your existing NOW account details).
You could also try both the supplied power adapter that came with your Stick and also try a USB port on your television for power to the Stick if that makes any difference.
To use power from your television USB port it needs to be 5VDC 900Ma or higher, some older televisions may only have 5VDC 500Ma which will be insufficient.
