Can ping Arduino Ethernet but cannot connect from browser or other client

I have an Arduino Nano with a piggyback Ethernet shield running a small server sketch that shall communicate with a VBA script which uses Excel to register the status of the Arduino. This worked very well until 2 days ago. I could send and receive html messages between Arduino and my laptop. Then suddenly I had a problem to connect my laptop to internet, so I tried to resolve this problem, which is apparently unrelated to the Arduino test. I don't remember exactly what eventually resolved the internet problem, I think it was some kind of a network reset that I was advised to do.
But at this point my VBA script could not establish a connection with the Arduino anymore, all attempts timed out.
Anyway I could verify that the problem was not the Arduino itself because I could connect to it via a browser and the response was correct. Neither was it my VBA script because using an internet URL like instead of the Arduino IP, I could connect immediately.

Now I have tried to recover the connectivity between the Arduino server and my client script by trying several different settings and the result is that I cannot even connect to the server with a web browser anymore. The more I try, the bigger is the mess getting.

The Arduino server is still up and running, I can ping it and my IP scanner finds it also.

I am not adding the server and client code here because I think this is irrelevant, the communication between them was fine before resetting the network.
So this is quite obviously a setting problem of the local network. I am not a network expert so I need urgently help from savvier people.
Can anybody help me, please?
How could I start the analysis, what should I do to recover the previous situation when everything worked just fine? Unfortunately there is no restore point available that would allow me to simply go back to the previous settings.
Let me add that I have two laptops with windows 10 in the local area network and neither can see the other. I have not been able to resolve this either. So there is obviously a LAN setting problem.

This can be almost any local network problem. I'd (wildly) guess that you activated network isolation (or however your vendor calls this) so that every device on the network may access the internet but not any other device on the local network.

If you have a friend or co-worker which is a network expert, install WireShark on a notebook, offer him/her a good dinner and start debugging your network.

If you have no access to knowledgeable person you still have the hard way: Reset your router to factory defaults, re-enable the internet connectivity using the documentation of your provider and most probably you have your old connectivity back.

Thank you pylon. I already downloaded Wireshark, will see if I can resolve the problem. Unfortunately I have no knowledgeable friend :confused: