A clicking noise suggests the starter is being energised, so this discounts the transmission interlock.
My guess is its suffered from a failed crankshaft, which is pretty common, and normally results in an engine that won't turn over. A failed oil pump casing is also common, but usually the engine will still crank over, as it normally just bends valves, or breaks rockers, when the timing goes out.
Unless you're an experienced mechanic, or experienced in D3 repairs, it's probably not a good project to cut your D3 teeth on, let alone the work involved sorting a replacement engine will often exceed the value of the repaired vehicle.