Hi bnour,

This issue could be due to the applications running in the background which start working once you're connected to the internet. Restart the system to safe mode with networking i.e restart PC , tap at Dell logo and select 'safe mode with networking' . Once it boots , connect to the internet and check the CPU usage. If the results show normal then , update your antivirus and run a complete scan.

You can also do a clean boot, Click Start, type msconfig.exe in the Start Search box, and then press Enter to start the System Configuration utility.

1. Click on services tab , enable check box Hide all Microsoft services, then click on disable all button.

2. Click on Startup tab and uncheck all the unwanted applications which you do not want them to load during startup, including messengers apps, browsers, updates, desktop enhancers etc.

3. Uninstall the applications which you do not use from your PC, including toolbars, 3rd party apps etc.

Restart the system and check for the CPU usage.