Best way to tell is put some water in the tank and try it. It may take a few minutes to purge the air from the system but then you should get a more or less steady flow and good pressure. If the tank was empty but the pump was NOT running, there shouldn't be any damage. Merely having the switch on doesn't mean too much as the pump will cycle itself when the pressure drops. If there was enough pressure remaining in the line to shut it off, you should be o.k. This is assuming your pump isn't designed to run continuously whenever the power is switched on.
In addition to what Karl suggested it may be necessary to hook up to site water to get the pump to prime. This may or may not be necessary. First thin I would do is turn the pump on and listen to see if it runs.
Depending on the pump manufacturer, if your pump is indeed damaged, try call ing the customer service people of the pump. Sometimes they accomodate customers with replacement parts. The worst that can happen is they charge you for the parts.