R. T. France writes in his commentary of this verse, ". . . for most people the healing of a few invalids by laying hands on them would hardly constitute οὐδεμία δύναμις" (244).
It is an interesting matter in the Gospel of Mark that he would retain this phrasing of the passage, especially when the Matthean parallel only tells us that he did not do any miracles there, as though it were more of a choice on Jesus' behalf (Matthew 13:58). The end result is ultimately the same - there are miraculous acts which could have happened in this scene that are now absent as an end result of lacking faith. Still, our question should rest upon the Why of the passage just as much (if not moreso) than the What. If we take Matthew's version at face value then we would have a simple give-and-take with Jesus and those who fail to believe: Jesus comes, they don't believe, he doesn't do any miracles there. But Mark's version forces us to deal with the raw and somewhat unsettling notion that Jesus' miraculous activity was prevented by the presence of such stark unbelief.
Modern Christianity seldom accommodates for this sort of thinking, instead wishing for more Platonic understandings of God which see him as perfect and immutable - he cannot be changed, he cannot be moved, and his will is never thwarted. That's the very essence of God in the minds of many. We think these things because we believe that divine perfection necessarily brings a changeless existence, as any change would then be for the worse. The Ancient Near East did not conceive of divinity in such terms, and the biblical ideal is more Semitic than Platonic in its approach, so it is Western philosophy that must adapt. Suffice it to say, this passage becomes a problem unless we learn to read it in its proper context.
Disbelief is an something which modern minds most often fail to understand. But it is part of a larger spiritual war that is being waged. And if we are to understand that belief is a powerful entity that can impact the world, then why do we think that disbelief is an impotent option? It is part of the battle. Mark knows this (and so does Matthew), and places it in the center of the kingdom activity surrounding Jesus. The greatest obstacle in his way was not the synagogue leaders, it was not the Sanhedrin's questions, it certainly was not the Romans, and it is not the cross and his gruesome death. The single greatest barrier between the kingdom of God and an unrestored world is disbelief in the power of that kingdom.
This is why the single greatest problem facing churches today is apathy from within congregations, who fail to see the life-giving potential of the Spirit within them. It ultimately amounts to disbelief as a distinct act of spiritual warfare, stopping the very power of God.
Now, back to France's comment regarding the ironic juxtaposition of "no miracles" and the exception of "healing a few who were sick." By standards both ancient and modern such miracles are awe-inspiring - they are not commonplace. (That is why they are miracles.) France points out (as do some other exegetes) that this is an indication of the 'minimizing' of Jesus' miraculous activity due to the lack of faith. But notice how the power of God seems to be running on a dual perspective in this passage. There is a point of view which seems to indicate that the miracles are indeed significant (and they undoubtedly are). But there is another which is telling us that this messianic figure is constrained in what he can do. One could easily ask the question, If this is what Jesus' activity looks like when he cannot perform miraculous deeds then what would his work look like if he were set loose?
I'm not sure if this is what Mark intended for this story to become, but it appears to have turned into a metaphor for the church. We have such widespread disbelief (often due to the factors we mentioned above) that the one or two or however many miracles we see in our own lives appear so few and far between than what we read in Scripture. The spiritual warfare is raging more now than ever before because of the rise of apathy in our culture and disbelief holding back the power of God. Yes, this is precisely what France refers to as "christologically striking" in that the work of God is stopped (in this one place) by the power of disbelief.
The work of Jesus moved on to another town, another group, another region . . . as it always did. Just like it is doing in evangelical Christianity, who is doing more today to demonstrate faith in political solutions and environmental initiatives than it is in the power to believe in the kingdom of God and the power of his Spirit.