Ok, turn your system "on" so that the pump should be running...
As you have a centre screw in the pump; use a large flat-bladed screwdriver to remove this "cap" - DO NOT LOOSE IT!
Now take a smaller screwdriver and insert it slowly into the hole where the cap covered... Be careful because if the pump is running, the screwdriver blade will grab and get caught on the pump impellor - Be ready to withdraw the blade quickly...
As you insert the screwdriver, if the pump is not actually running, the screwdriver will bottom out without getting spun by the pump... Where it bottoms out is a slot, which you need to engage the screwdriver into and attempt to spin the impellor blade... This is like "jump-starting" the pump... You may feel the pump kick into life again and everything is fine, otherwise you might just feel the resistance of the pump motor "trying" to turn the impellor, but not quite managing it... If this is the case, new pump time I'm afraid.
Once happy, place the cap back in.
WARNING:
When you take this cap off, a small amount of water will escape from the pump constantly if the system is properly filled... Make sure you have a towel or "wet-sheet" handy.
Best of luck.
ccMods
July 2006