In 877 a Danish Army at Exeter was blockaded by Alfred the Great and bad weather and heavy seas kept the reserves from landing in Devon to relieve the pressure and win the day.
My POD is that the weather that day was calm (Somebody stepped on a butterfly in China I guess), the Viking fleet landed, Alfred's army was routed and Alfred himself was captured and killed. England is effectively conquered as they have no strong leaders to mount a resistance (and definitely no healthy ones, even Alfred was sickly) and the Vikings don't convert to Catholicism.
The Normans start settling into France in the 880's, but this time with a strong and friendly Viking neighbor to their north instead of the Christian Saxons. Having England as a more southern naval base, any expeditions across the Atlantic are less harassed by sea ice, making further colonization in America possible.
As time continues Christian pressure is subverted to some extent by the still pagan Normans, but is still powerful enough for Jesus and God to be incorporated into the Norse Parthenon. Viking power is spread throughout Northern Europe and Northeastern North America, and many pagan "sects" appear, usually with heavy local influence.
I have no idea how to make Islam less influential from this POD. Maybe as the Muslims move into Byzantium the Kievian Rus can stage raids and get more Viking raids on the Muslim lands for wealth, but I find it kind of unlikely since it'd be pretty out of their way (No Norman Sicily since they weren't Christian and didn't fight in the crusades)