Did you add enough water in your fresh water tank? The pump might have pumped it dry if you didn't put enough water in the tank to start with.
Also, keep water heater in by-pass until you know lines are pressurized and flushed from the winter "pink stuff" (if you used it), before opening the water heater. Otherwise, the water heater will need to fill first before you have pressure.
I do it this way with water heater in bypass.
1. Turn pump on.
2. Turn on one faucet (cold) only until it runs.
3. If it does not run, close faucet and turn off pump.
4. Turn pump on again, it will pressuize and turn off.
5. Turn on faucet (only cold), until air is pushed out. Turn off. Wait for pump to stop. Do hot next. Same procedure.
6. When you flip your water off by-pass, it will fill until the lines pressurize again. Wait for pump to stop. Then open hot faucets to allow the air to bleed out of the water heater.