My sump pump is only 3 years old and it won't stop running after it has pumped the water out of the sump pit. What do I do to fix this? Is there a switch that I have to adjust?
Please help.

Your sump-pump may have some debris tangle up around the float. Remove pit cover and visually inspect the pump and the float. Take garden hose and wash the pump, float and pit.

Sounds like the float might have a hole and is waterlogged or the switch inside the float is bad. Does picking up the float stop the pump? If it does, check to see if the float is replaceable.