Can there be a Communist vs Capitalist style cold war happening without a Second World War.
I would say definitely yes. The PODs you mention do in no way make the USSR less dictatorial and totalitarian, and in all probability more aggressive against other countries. On the other hand, the PODs in no way remove the people who brought about the European process of unification, and the fact that Hitler dies may very well lead to these people coming into power earlier. So you may get an earlier unified Western Europe co-operating with the USA and possibly Japan, China and Turkey against the USSR.
for a POD Maybe Hitler dies and Weimar trundles on, and the USSR captures Poland and sways some other states thanks to that in 1920.
If the USSR conquers most of Poland, and Germany takes the opportunity to reconquer the territories lost to Poland at Versailles, then there is no alternate Cold War, but some kind of balance of power system, with Britain and France (and potentially, the USA) on the same side, but opposed to Germany just as much as to the USSR. If the USSR conquers all of Poland and even more countries, then it becomes quite likely that Britain and France unite with Germany against an overwhelming threat.
What would the world be like with a cold war starting two decades earlier.
What would the world look like if the USA didn't become a Superpower or would it get involved to fight against communism. Who would be the main opponents of the USSR, what would the flash points be like. How would the British empire go about and colonialism as a whole.
The USA would be an economic superpower in any case. The PODs you mention would not remove the military intervention of the USA in post WWI Soviet Russia, and it seems next to impossible to me that the USA turns in any way pro-Soviet. US forces in Europe do not seem very likely to me, neither in the case of a three-sided balance of power system (Franco-British alliance / Germany / USSR) nor in the case of an alternate Cold War with Britain, France and Germany allied against the USSR. The balance of power system would be too similar to what happened historically to remove US isolationism, and in the alternate Cold War, Germany and Japan would be much stronger opponents of the USSR than they were in the OTL Cold War, which largely removes any need for US forces in Europe or Japan.
If we have an alternate Cold War, what could bring about a more active involvement of the US in power politics, is an alliance between the USSR and Japan, or a USSR / Japan / China alliance.
One big difference between the alternate Cold War and the OTL Cold War is the fact that the Red Army is not where it is because it has defeated Hitler, so the Soviet Union would be seen as a foreign aggressor even earlier and to a greater degree than it was in OTL. The same is also true for the legitimacy that Stalin's regime had gained in the eyes of the Soviet population, because he had been the leader in the war against Hitler. This kind of legitimacy would not be there in the eyes of the peoples of the Soviet Union in an alternate Cold War.
I think that colonialism would end at roughly the same time, and for the same reasons that it ended in OTL.