We just put in a hot water heater in and we had water pressure before we installed it now we only have a trickle. We don't have the electric hooked up yet. But once we filled hot water heater with water lost the pressure all together. What could we do to figure out what went wrong?

Sounds like you let trash get in the line. Disconnect pipe nearest water heater and turn on water for a second or two to see if water comes out, then move down line. You also may remove the screens on faucets to clean out trash.