Where did you find it?
In the Finder MenuBar, click on Finder > Preference and click the SIdeBar tab.
Make sure that the Hard Drive button is checked in the top pane and the Desktop button is checked in the bottom pane.
That should put your icon back on the desktop
P
Computer was in Sleep Mode I touched some buttons on keyboard to wake it up and when it came back on My Hard drive icon had disappeared. When I searched for it, it said it had been modified. I copied the icon but can I restore the original icon?

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