This is either a power issue or the motor thermal cut-out has tripped.
First, confirm power. Make sure the unit is plugged into a grounded outlet, not a GFI outlet that's tripped or a switched circuit controlled by a timer. Check the On/Off switch is in the On (I) position.
If power is confirmed and it's still silent, the motor overheated and needs to cool. Unplug it. Wait 20-45 minutes. Plug it back in and try.
If that didn't work, inspect the cord and plug for damage. Never operate with a damaged cord. If damaged, contact Vitamix Customer Service at 1.800.848.2649 immediately.
Heads up: Do not supply power through an external switching device like a timer. It can cause the thermal cut-out to reset improperly.