This may be a hard one to replicate but it seems to occur about 50% of the time.
Executing an Explain Plan in the same Editor as a running query will lock Toad (screen refresh freeze) and the results of the Explain Plan will not display until the first records from the running query begin to appear in the result set. If your query doesn’t return rows for 10 minutes then that is how long the screen-refresh freeze is. No user action can occur until the screen-refresh freeze ends. Please note that Toad itself does not produce any error mesage of any kind before or after the event. Once the screen-refresh freeze returns to normal, Toad functions normally.