In addition to manually priming it, you can also try the technique suggested here:
Machine has lost its prime
Turn the machine on but leave brew and steam switches on right OFF. Place a cup under the steaming wand. Open t he steaming valve. Now, although we did not heat the boiler for steam, the wand has this second function, namely priming the pump. When the valve is opened but the boiler is not heated for steaming, the pump kicks on and primes the pump. When the water from the wand is flowing in a continuous stream (3-5 seconds), shut the steam valve. You may now heat the water to steam or brew.
If that doesn't work, pull it apart and inspect all the tubing.
If that doesn't work, post everything that you've tried here. Can you hear the pump running?