Diagnostic Environment (Windows booted into "Safe Mode with Networking", connected to router via network cable; WiFi turned OFF in router; all other devices disconnected from router; VPN/remote links disconnected from router)
Note: to boot Windows 8/10 into Safe Mode click here
Network monitoring - can be run immediately, without entering "Safe mode"
You can view the historical logs for network usage in a few simple step:
Click the Windows logo (start) > Settings
Select NETWORK & INTERNET > Data Usage
Click Usage details to view historical usage for individual applications
Monitor the network traffic live
Monitoring the network live can be done using Task Manager (Ctrl + Shift + esc).
Click the Perfromance tab...
...now click the link Open Resource Monitor to get a detailed view of which applications are consuming bandwidth