How to check the event log (if any) for network failure?
In case you just need to know when internet access was lost / restored regardless of state changes of various network devices, navigate to UTC in Event Viewer:
Applications and Services Logs/Microsoft/Windows/UniversalTelemetryClient/Operational
Look for event ID 55. It displays a friendly text "Is the Internet available:" followed by true or false.
You can type at the command prompt:
netsh wlan show wlanreport
An HTML report will be generated, containing the logs of the last 3 days. In the "Summary/Wireless sessions" section, you can find informations about relevant activities.
The path to the generated report will be printed by the tool, by default it tries to write to C:\ProgramData\Microsoft\Windows\WlanReport\wlan-report-latest.html.
In the event viewer we can enable logging of WiFi. It gives detailed logs of the signal strength of WiFi.
The complete process including screenshots is given here.
Open the Windows Event viewer (eventvwr.msc) and then within the View Menu enable the Show Analytic and Debug Logs options.
Navigate to the WLAN-autoconfig event log. Since we enabled the Analytic and Debug logs option, beside the Operational log we also see the Diagnostic log.
The Diagnostic event log by default is not enabled, so first we have to enable it by right-clicking -> select Properties.
As soon as the Diagnostics mode is enabled you should see events coming in. To enforce things a bit simply disable and enable your wireless connection using your vendor's wireless connection software or by pressing the hardware button on your laptop.
You can see when the WiFi signal is lost.
I use Windows 10, and in my event viewer under Applications and Services Logs/Microsoft/Windows/NetworkProfile/Operational I find the event IDs 10000 for connected to a network and 10001 for disconnected from a network.