Windows users try this:

Ctrl-Alt-Del then launch TaskManager.

In TaskManager, click the "Performance" tab and see the simple stats.

While on the Performance tab, then click the ellipsis (. . .) menu, so you can then open ResourceMonitor.

Then close TaskManager.

In ResourceMonitor, under the Overview tab, for the CPU click the column header for "Average CPU" so that the processes using the most CPU are shown top-down from most usage to least.

In Overview, for Disk click the Write (B/sec) column header, for Network click Send (B/sec), and for Memory click Commit (KB).

Then under the individual CPU, Memory, Disk, and Network tabs click on the similar column headers. Under any tab now you should be able to see the most prominent resource usages.

Notice how your CPU settles down after a while of idling.

Then click on the Disk tab to focus your attention on that one exclusively.

Let it sit for 5 or 10 minutes then check your CPU usage. See if it's been climbing gradually higher while you weren't looking.