turn signals dont work what causes this

Likely causes are bulbs or flasher relay. Both cheap and easy to replace. Least likely is the switch itself, but also possible, and worst case a wiring issue due to age and corrosion (lets not go there). If it happens equally on both directions, I would replace the flasher unit first ($5.00 part). Pick one up at any auto parts store and ask for their help in finding its location under your driver's side dash. Once located it should just pull out from a holding clip. Unplug the wires and attach them to the new unit and put the new unit back into the holding clip. Job done.