if you have drained the system, tried to run it empty, and now water does not circulate, then you may have an air lock, or air in the pump, or the pump might be seized (from running without water in it and overheating)
Apart from bleeding air out of all the rads to verify they are full of water, undo the large screw on the front of the pump. Some air may escape, then a few drops of water may trickle out. This is OK. Now look through the hole where the large screw was, and you will see the motor spindle. When turned off, you should be able to turn it with a screwdriver. When turned on, you should see it spinning. What do you see?
When turned on, is the pump strikingly hotter than the pipes around it?
I am not a pro