If you're able to see your device listed in the Devices tab but the Dashboard isn't functioning and there is no timestamp of data received in the Home tab next to Download Data, the system has never received data from the device. You can confirm this in the Devices tab by clicking Edit next to the device in the list. At the bottom of the panel, where you should see the last data received it will say "device never seen".
The most likely cause of this issue is missing Python or MQTT libraries. Go back through the install process and make sure you followed each step carefully to install all needed packages. Raspbian does not include them by default.
If you're continuing to experience issues, check out this FAQ.