My Simple Remote has stopped working

The basic remote really is basic. It is IR (infrared) only, and requires a direct line of sight to use. You mention it will work if the remote is directly in front of the Roku. Is there any direct sunlight hitting the Roku? That can interfere with the IR signal. Also, not every Roku remote has the batteries oriented the same way. Some are inserted in the same direction, while others face the alternate direction. Make sure you haven't inserted the batteries incorrectly.

You can test the IR remote by looking at it through a digital camera, such as a cell phone camera. When you press any remote button, you should see a flashing light through the camera viewer. If you don't see the flashing light, and you're certain the batteries are in correctly, then the remote has likely failed. It isn't common for them to fail, but as with any electronic device it's always possible.

If it has failed, you have a couple of options. You can get a new Roku remote from almost any store that sells Roku products, such as Best Buy. I don't know for certain if your Roku Express supports using a WiFi Direct remote (that would be the voice remote) but I don't think it does. Another option would be an inexpensive universal IR remote which can be found almost anywhere electronic devices are sold. I've seen them for less than $10 in many stores. Just make sure the packaging shows it supports Roku players.