Hi all, thanks loads for all the help in the past. Now I have to ask for your help once again as my golf is refusing to start again.

When I turn the key I hear the furl pump prime for the usual amount of time but all I get when i try to start it is a loud clicking from under the bonnet, it seems to be coming from the starter motor, and the engine doesn't turn over. I have read about the solenoid in there clicking or something, i guess it copuld be that? I tested all other electric things in the car which seem to be working fine except sometimes when the battery power seems to be intermittent - ignition lights flash on and off and a relay ticks on and off in the fuse box too. When the car was in this state I tried the electric window and that was intermittent too, like it was jerky but uniformly so, in time with the ticking.
My earth wires seem to be ok, except the one from the bonnet to the body (surely this won't affect anything) The main earth lead from battery to gear box is a year old.
Car was running well before.
I read obout rocking the car in gear, do you think this will work? going to try it tomorrow- at work at the moment, I tried to jump it with leads yeasterday but no luck. Also gave the starter motor a good wack or two but maybe i should give it a bit more, starter motor is well rusty so perhaps a new one could be in order? are they expensive?
I checked all fuses, they are ok, could it be a relay problem?
Sorry for the long post, hope someone can help..