I set up my express and it comes to the purple screen with ROKU bouncing up and down then about 30 seconds it goes off and back on. I have reset the box, my internet, unplugged and re plugged. Changed the remote batteries and tried a different tv but it will no pop up the activation screen automatically like the instructions say.
Are you using the supplied power adapter?
yes
There was a guy that said replacing his HDMI cable had an effect. I wouldn't have believed it, but it's worth a try. Beyond that, try to get it replaced under warranty.