The only way, from my understanding of things, for Germany to have won WWI and taken France, is this:
-The Willy-Nicky telegrams actually manage to avert conflict between Germany and Russia, even if Russia decides to mobilize against the Austrians over Serbia.
-The Schleiffen Plan goes as it should have. This means that the Germans are more aggressive in Liege, they invest Antwerp to busy the Belgians, but not to the extent they did OTL. Also, when the armies move closer to Paris, the wide left hook is taken as necessary to strike at Paris from the south, instead of the tight hook used to bring about the battle on the Marne.
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And even if that happens though, I do see the following occuring as well:
-If Germany tries to take French colonies in the Americas, there's the possibility the US would invoke the Monroe Doctrine, drawing hte US into second phase of the war alongside Russia and Britain. Of course here, with the US going to war in 1915 likely, Wilson cannot manage to get elected in 1916, so who takes charge there, is there any chance of TR running, and winning, in that election?
So yes, it is possible, I think, for a German victory in 1914 over France, but only at the expense of an American theatre in South America and Africa as the British (in Africa) and the US (in South America) try to reclaim French colonies, either for themselves, or to return to France.
That brings up a question though...in this possible African campaign...how likely is it that there'd basically be a Second Fashoda Crisis, which actually -does- devolve into war between the UK and France?