There are few reason that may cause your machine not to grind. There are:

1) The coffee quantity dial may be in the pre ground use coffee setting which will bypass the grinder. This setting is used for tamping only.

2) Please check the My Coffee icon to see if it is flashing. If this is flashing it means the My Coffee program is in programming mode. You must complete the program in order to activate the grinder.   

3) Lastly, please be sure the filter holder is inserted tightly to activate the grinder