How to handle end of game clock situation

[ronny mulkey]

5.0 seconds left on the clock
division line throw in
throw in completed into the team's front court
dribble to basket
subsequent shot
ball caroms off rim
still 5.0 seconds left on clock
Timer admits that the clock was never started
officials have no count or definite knowledge of time elapsed

What do you do? Do over? Or, go to rebound and finish from there?