'73 3500Auto WON'T START!!! - PLEASE help me get my 3500Auto started!

I'm stuck without a mechanic in frozen cold Berlin, Germany! My battery shows 12volts at the terminals. It should too, it's only 14 months old! The starter motor solenoid just clicks rapidly and very loudly like machine gun fire. What do I check for next? What equipment or tools do I need? I can barely change a light bulb, but I'm keen. Any patient person(s) want to help me get my car going again?
I know the vacuum advance unit on the distributor doesn't work, can't get a new one until early January... To compensate that my mechanic advanced the timing by rotating the distributor, which incidentally contains a Lumenition LED unit instead of normal points. He's now in Blighty until the new year... and even with a jump from another car (revving) it wouldn't 'catch', just cranked...
Did the engine actually crank when jumped by another car? If so, your battery or charging system isn't up to scratch, or you have a leak to earth somewhere, or something is stuck on, like the boot light.
Did the car run ok after the ignition was advanced? The vacuum advance will not have any effect on it starting. Assuming it did run ok, and it did turn over when jumped, then you have either no spark or no fuel.
If you have a haynes manual, there is a fault finding bit in there which will guide you through.
If you don't have a manual then post again and hopefully someone will come up with the answer.
Measure the batery voltage with the headlights on main beam. I suspect that the battery is discharged. It will show 12 volts with little electrical load.
Check the earth connection (-ve) from the battery to the car body. It must be good, bolted to clean bright metal. Try taking a jump lead from the -ve terminal to a good earth, the hole on the bottom boot lip where the boot catch engages is usually clean and will take a jump lead terminal. Hopefully with a charged battery the engine will now crank, if it does improve things then the earth lead needs attention If you are jump starting with the leads from the other car direct to your battery terminals and your earth is poor then you will achieve very little benefit; with the battery so far from the engine it needs every volt it can muster..
If you have been trying to start the car for some time and failed then I would suggest cleaning the spark plugs as they tend to get sooty / wet, better still put some new ones in.
Hope you get running soon ...
Thanks everybody who posted useful suggestions. I'm mobile again!
A 24hr slow charge provided my battery with enough oomph to spark the old girl into life.
Now I suppose I have to check if the alternator is working properly or whether there is a bad earth somewhere...
Might my tilt/slide steel sunroof be the cuplrit? It has taken to opening of its own accord, especially in the rain! Don't know where the fuse is. Should I disconnect the sunroof open/close toggle switch, which is next to the rear window demister. Will it remain closed then?
Look forward to further sage advice! Happy New Year all.