I have Node-RED running on a raspberry pi that is hardwired to my router. My PC is also hardwired.
My internet recently went down and I could not get Node-RED to load (http://192.168.1.100:1880/) on my PC. Is this normal ? It was weird because other pages being served from my Pi would load.
Node-RED itself "should" be ok totally disconnected. If there is a node that is blocking it then that ought to be investigated as it ought to still allow the flow to run.
the console when you run Node-RED is the log - but I would suspect that unless we are lucky the node wouldn't report anything... but it's worth a look.
Which 3rd party nodes have you got installed may be easier to guess from.
start Node-RED with the --safe flag - which will start the editor but not run the actual flow... so you should be able to browse/edit the flow (and then hit deploy to start it).
remove the node from the flow - and see if it then starts.
Finally - uninstall the node and restart Node-RED - and see if it then works.