The Germans may have won the war but the following reasons blocked them from winning.
Hitler had no luck in enticing England to join them in the war against USSR.He had to opt for less powerful countries to support him.Italy was another powerful country because they had the same ideology as the Nazis but their equipments was already outdated at that time
After their failed attempt to capture Moscow,Hitler saved germany by ordering troops to stay and fight against Russian counter attack. After this,Hitler felt vindicated and took this withdrawal policy too far.In later battles,he denied the army to pull out to more favourable terrain and this caused German armies several casualties.
The Germans had advanced technology compared to other countries and instead of mass producing this equipments,the quest for heavier tanks cost them
Hitler declared war on the USA and that was Godsent for churchill and Roosevelt who soon agreed on German first strategy which meant the destruction of Germany took precedence over Japan
Hitler did not listen to his generals,he took over as the commander in chief.He considered himself a military genus. If anything goes wrong, he blames his generals for not following his "brilliant ideas"
Hitler was certain of quick victory over the USSR .He didn't take into account the Russian cold.After they were unable to capture Moscow,most soldiers faced the full onslaught of artic cold in their summer uniforms.
In conclusion, the Germans may have won the war if not for the mistakes highlighted above and some other ones which I have not included in this write up.