The Normans were Danish Vikings. The Danes did invade all of Western Europe, as far as the Maghreb. One group managed to obtain land from the King of France and became known as the Normans. They adopted French language and customs and combined their own Norse technology to the French one.
I suppose that they became more powerful because they had enough land to support their future conquests. They didn't have to go back to Denmark to make new weapons or bring more men, but could just recruit local Frenchmen, and get all the food and weapons they needed in Normandy.
The nearest place to conquer outside France from their new "base" was England, just across the Channel. Furthermore the kingdom of England was already weakened from the war between another group of Danish Vikings and the Anglo-Saxons. The Normans came with a big army combining Danish and French troops when England was already on its knees. The timing was perfect.
Another reason they didn't venture more inland (like Switzerland) is that Vikings were primarily sailors. Their ships could go up rivers, but not upstream in mountainous areas.