Hello Dave and welcome to the forum.
It's difficult to get a good sense of what you are seeing. Can you provide a screenshot to help us understand better?
Are you saying that File Explorer opens automatically when you boot into Windows 10, or....
Are you saying that when you open File Explorer manually, it defaults to a particular folder?
Use the View menu and the options Icon to change folder and search options. Then use the general tab to switch to "This PC" in the drop down at the top.
Close and open File Explorer again. In the navigation pane collapse everything except "This PC". In the right viewing pane collapse everything except "Devices and drives"
Close and open File Explorer again.