@DavWav6169 welcome to the forum.
It sounds like Joplin is running but for some reason is displaying outside your screen boundaries.
One thing you can try is to properly shut down / quit Joplin and have a look at C:\Users\<username>\AppData\Roaming\Joplin\window-state-prod.json particularly the values "x" and "y". This is the top left origin point of the Joplin window. If any are values greater than your screen width and depth change them to something like "x":10,"y":10 and restart Joplin.