The incoming water pipe under my kitchen sink is leaking at the joint of the shut off valve how can I fix it?

== cut off the water == drain the pipe -- make new connections using the ""purple PVC pipe glue"" the dish wash machine has no bearing on the on/off pressure .. you may have higher pressure to the house than when it was built and that is a phone call to the city water dept .... you can get a pressure control for the house that will lower the PSI of the water and lessen the chance of this happening to another H2O`outlet in the house ....