On some WaterRower machines, the case of the S4 may block the USB cable from firmly connecting to the mini-USB port, preventing the Ergatta app from detecting the S4 (and triggering the "No Rower Connected!" alert). As a workaround, you'll want to hardwire the USB cable into the port:
Using a screwdriver, remove the screws from the battery section on the back of your S4 monitor. Remove the batteries.
Then, remove the remaining 4 screws on the back of the S4:
Gently lift the top of the S4 open. String the USB cable through the jack and plug directly into the mini-USB port on the face of the S4.
Make sure your tablet monitor is powered on and the other end of the USB cable is plugged into the tablet. The S4 monitor should turn on automatically, and you should no longer see a "No Rower Connected!" alert. Reassemble the S4 and add the screws.
If the S4 monitor does not turn on, then you may need a replacement S4 monitor. Please reach out to support@ergatta.com to request a replacement.