Serial mouse has disappeared

[ChigleyBill]

Hi
I'm trying to provide support to someone using XP pro on a Dell laptop. The external serial mouse which was connected and working last week has disappeared. I can't find how to add it back.
Any advice gratefully received.
Thanks

[ChigleyBill]

Ok
Don't know why it had disappeared but, if you go to Control Panel>System>Hardware>Device Manager and right click on Com Port 1 and select Scan for Hardware Changes, that seems to fix it.