I have a user that is having problems with AutoSum updating after a cell is deleted. He has the following...

100
200
100

400

If he deletes one of the cells, (lets say 200), the autosum number stays at 400. I reinstalled his MS Office and it worked for a few days, but now he is having the same problem.

So now he has...
100

100

400

Any suggestions would be greatly appreciated, as this "user" is my boss.