I have a ROKU Express. Suddenly on my 2nd device it said not connected, and the screen saver had an ad for $24.95, but didn’t say what for, then the remote stopped working. Now the ROKU doesn’t even come on.
The remote that comes with the Express is a direct-line-of-sight infrared (IR) remote that must be pointed at the Express. Make sure that the Express is located where it can be seen from your remote location, and that the front side of the Express where the IR receptor is located is pointing out into the room. Also make sure there's nothing in front of the Express blocking the signal from the remote.
The "not connected" message refers to connecting to your home wifi network. My Rokus occasionally drop their wifi connection, but here's how I get it back (this DOES require a working remote):
Restart your router (even if other devices have no problem finding and connecting). Sometimes that's all it takes, if not keep going.
Restart the Roku to clear its memory via Settings > System > System restart (for a Roku TV it's Settings > System > Power > System restart). Again sometimes that's all it takes, if not keep going.
Find and connect to your network via Settings> Network > Set up connection
If that doesn't fix it, try disconnecting the power to your Roku for a few seconds. When it comes back up, see if you then can set up the network connection.
Also, Roku models Express, Express+, Premiere, and Premiere+ cannot connect to the 5 GHz wifi band, only to the 2.4 GHz band. If you have a dual band router with both 2.4 and 5 GHz bands, be sure the router's 2.4 GHz band is turned on.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." Note: I am not a Roku employee, just a user like you.