My nissan it turns over but has no spark and it wont start

If you have a 12 volt test light put the point on the positive lead to
the coil and the ground lead to a good ground ( Negitive side of battery ). Then turn the key on. If the test light comes on then you have power to the coil. With power to the coil confirmed have someone crank the engine and put the test light on the negitive side of the coil. The light should flash at a rapid steady rate. If not then your pickup in the distributor may be bad. If no power to coil with key on or when cranking you may have a bad ignition switch.
Another way to test for spark is to remove the coil wire from the dist cap and hold the end close to a ground ( 1/4 inch away) and
have some one crank the engine. If you get a good spark but no
spark to the spark plugs you may have a cracked dist cap or a bad rotor. If no spark at coil wire use a wire in place of the coil wire to check for spark. You may have a bad coil wire. Good luck. Neil W.