If you take a 3 gallon bucket and pour it directly into the bowl, does it create the suction to empty it?
If not, you may want to pull the toilet and check there isn't a clog. I had this happen and when I pulled the bowl off the seal, I found one of my daughter's friends had flushed a handful of q-tips and they were jammed into the drainage tube, grabbing all kinds of things.
If it does drain, then check the holes around the top of the toilet where the water flows to start the swirl process. They will be under the rim and angled to flow the water properly. Make sure they aren't clogged. Next, check the water level in the tank and make sure the fill up valve wasn't set too low and not flowing enough water.