It's a familiar story: A family buys a new home and, after the first winter, all the stones in the flagstone walk seem to be climbing out of the ground. Footing is treacherous, mowing the lawn even worse.
What happened, in most cases, is that the builder laid the stones right on the ground without preparing a suitable bed, and frost action heaved everything out of kilter.
If this is your problem, the only solution is to lay it again, Sam. the repair will be fairly easy, though, since the walk is already laid out and the stones fit together properly. To start, remove all the flags and place them beside the walk, keeping them all in the same relative positions so you can place them in the right order.
Then dig out the area of the old walk to a depth of about four inches, Actual depth can vary according to the thickness of your stones. A good rule of thumb is to dig to a depth equal to the thickness of the flags plus 2 1/2 inches.
When the digging's done, put down a two-inch layer of sand or stone dust. Rake it out level, dampen slighty with the mist from a garden hose, and start replacing the stones on their new bed. Place each stone carefully, adding or digging away sand as necessary to get a good fit with no rocking.
Walk around on each stone after it has been placed. If you can feel it shift under your feet, its bed needs to be adjusted. Then replace the stone and test again.
Once all stones have been set, fill in the cracks between flags with sand or stone dust. Pour sand on the walk and brush it into the cracks with a broom. Then dampen the sand with the garden hose. Take a board the thickness of the cracks between the stones and use it on edge to pack the sand down firmly in the joints; pound the board into the joints with a hammer. As the sand packs down, add more and keep packing.
You want the joints packed very tightly to keep the stones from shifting, and to discourage the growth of weeds.
When you're satisfied with your work, rinse the walk clean and let it dry. If the occassional stone comes loose and moves underfoot, remove it, releveled its bed, replace it and repack.
And don't worry: Once the walk has settled in it should remain smooth and level for years, without further attention.