Welcome to the forum @Gregor-Weissenborn.
In a terminal stop node red and start it again and then copy/paste the resulting log here. Copy/paste, not screenshot if possible please. When pasting it in use the <> button at the top of the forum entry window. You can stop/start node red using node-red-stop node-red-start
Starting as root systemd service.
Started Node-RED graphical event wiring tool.
4 Feb 17:47:02 - [info]
Willkommen bei Node-RED!
4 Feb 17:47:02 - [info] Node-RED Version: v1.2.6
4 Feb 17:47:02 - [info] Node.js Version: v12.20.1
4 Feb 17:47:02 - [info] Linux 4.19.108-v7+ arm LE
4 Feb 17:47:03 - [info] Paletten-Nodes werden geladen
4 Feb 17:47:10 - [info] [Dashboard] Started
4 Feb 17:47:10 - [info] Dashboard version 2.27.0 started at /ui
4 Feb 17:47:10 - [warn] ------------------------------------------------------
4 Feb 17:47:10 - [warn] [node-red-node-pi-sense-hat/sensehat] Error: Can't find Sense HAT python libraries. Run sudo apt-get install sense-hat
4 Feb 17:47:10 - [warn] ------------------------------------------------------
4 Feb 17:47:10 - [info] Einstellungsdatei: /root/.node-red/settings.js
4 Feb 17:47:10 - [info] Kontextspeicher: 'default' [ module=memory]
4 Feb 17:47:10 - [info] Benutzerverzeichnis: /root/.node-red
4 Feb 17:47:10 - [warn] Projekte inaktiviert: editorTheme.projects.enabled=false
4 Feb 17:47:10 - [info] Flow-Datei: /root/.node-red/flows_RaspberryPi3.json
4 Feb 17:47:10 - [info] Server wird jetzt auf ://127.0.0.1:1880/ ausgeführt.
4 Feb 17:47:11 - [warn]
Die Datei mit den Datenflowberechtigungsnachweisen wird mit einem vom System generierten Schlüssel verschlüsselt.
Wenn der vom System generierte Schlüssel aus irgendeinem Grund verloren geht, werden Ihre Berechtigungsnachweise
Die Datei kann nicht wiederhergestellt werden. Sie müssen sie löschen und erneut eingeben.
Ihre Berechtigungsnachweise.
Sie sollten Ihren eigenen Schlüssel mit Hilfe der Option 'credentialSecret' in
Ihre Einstellungsdatei. Node-RED wird dann Ihre Berechtigungsnachweise erneut verschlüsseln.
Datei mit dem ausgewählten Schlüssel beim nächsten Deployen einer Änderung verwenden.
4 Feb 17:47:11 - [info] Flows starten
4 Feb 17:47:13 - [info] Flows gestartet
4 Feb 17:47:13 - [info] [mqtt-broker:Raspberry Pi] Verbindung zum Broker mqtt://localhost:1883 hergestellt.
Built in 13.81s.
That is generally not a good idea, though whether it has anything to do with the problem I don't know. Running as root means that an accidental mistake in the flow could wipe your system.
Presumably you must have run the node-red installation script as root.
Have you tried clearing the browser cache? I should have suggested that last time.
If you temporarily move the flows file away and restart node-red then it will create a new empty flow. Having done that can you then add a ui node and open the dashboard ok?
Edit, just thought of something else. When you say you updated, what was it that you did?
Tried that.
Removed the flows.
(BTW: Last node can't be deleted. You have to create a new empty one to delete the remaining other one)
Deployed node-red-stop node-red-start
Added uinode
Deployed
Reloded dashbord.
Same result.
I had made:
apt-get update
apt-get upgrade
shutdown -r now
everything is running well again. - Thank very much you for your help!
Deleting the flow files (in /root/.node-red) did not help.
But deleting the whole .node-red folder helped.
Even that caused me to reinstall all the palette nodes, reconfigure some config nodes, and reconfigure the dashboard theme.
But that was the way that brought the dashboard back to life.
(No plan what in the update/upgrade of my Raspberry Pi caused the Dashboard to be unstable.)
That looks ok, I wanted to check where nodejs was installed from, in case your update and upgrade changed the major version. But assuming you didn't change anything else then I don't think it is that which caused the problem.
You could have saved some effort by copying the package.json from the original .node-red and running npm install
which would have installed everything you had installed.
It would be interesting to compare the new package.json with the old to see if there are any differences. The order in there does not matter.
That is a pity, it would have been good to understand what is going on for when someone else has a similar problem. It is difficult to do forensic analysis once the evidence has been destroyed.