Suddenly refuses to start,first time since i got it,plenty of fuel,good spark from plugs,fuses all ok,turns over perfectly but wont fire

If it turns, then the battery is OK. Either spark plugs are not firing in proper order (wrong firing order), no power to spark plugs, or no fuel because of fuel restrictions (dirty fuel filter). Inspect the air filter to ascertain its not clogged air. If you smell gas, then you saturated the spark plugs, which is why it refuses to run.
Let it sit for half hour to let spark plugs dry. Inspect to ascertain its not dirty spark plugs, which will also prevent engine from running. After ascertaining its proper firing order, spark plugs are clean, and there's power to distributor cap, ascertain there's fuel in fuel lines by squirting half second (short squirt) of starting fluid into air filter. Close the air filter housing to trap flammable starting fluid gas. Turn engine without giving throttle. Let starting fluid be ignited by spark plugs. If it won't start, then spark plugs are not firing to ignite starting fluid gas. If it starts briefly, but won't run when you give throttle, but catches when a 2nd person squirts more starting fluid into air filter just before engine stalls, then its a fuel restriction issue or no fuel in fuel lines.

Do you have spark, do you have fuel pressure? it is one of these or a camshaft timing problem. I would start with checking the spark at the plugs 1st.

Check the ECM/BAT fuse. this fuse controls the ECM and the fuel injection circuit. If the fuse is ok, you need to check for voltage at the spark plug. Pull the #1 spark plug. If the cylinder is getting fuel the plug will be wet with gasoline. Put the spark plug wire back on the plug. Now crank the starter and look for a spark from the spark plug electrode. If you can let me know what you find from these tests, I can help you determine the next course of action.

you didnt pull the distributer did you ? if so you could just be out of time. you also could have a fuse out , lots of cars today have a ignition fuse , check it .

could be crank shaft sensor, check for spark at plugs

check spark plugs and see if they are firing, if good then check the condition of the crank and cam sensors

there is no safety switch beside the fuses and relays how did you replace an engine, did you rebuilt it from top to bottom or did you just put another used motor in? if you replace it with another motor assuming you did not mess with the timing such as the belt and the camshaft, check and make sure you getting fire from spark plugs, having a friend turn the engine over and you observing the plug. by pulling one wire with the plug and ground it and turn the engine over and see if you getting any sparks, second check and make sure you getting plenty of fuel to the fuel filter and the fuel pump is working properly. no fuel to the filter, check fuel pump, good pump, faulty crank sensor. that is the first two thing need to be check, fuel and sparks. if no sparks, check coil if its good and putting out 12V, if its not, check the cam sensor, may be faulty. faulty cam sensor will not make spark plugs fire. if you are getting sparks and fire, than it out of timing, rotate the distributor forward or backward with small movement no more than a tip of a car key at a time, when you capture the running or sputtering of the engine, movement should be no more the a pencil lead forward or backward. without using a timing gun the best way to know if you have the engine on correct but close timing if you able to crank/start the engine and it fire right up without keeping the key turn.

the car wont start? do you mean the engine wont turn over or it wont fire or run? if the car does not run but it turn over, check the basic..see if you have sparks and fuel, then check all your fuse pertaining to engine and ignition. the car need to have both thing in order for the engine to run. If you getting both sparks and fuel you engine may have jump time especially with older car with high miles, it the sign timing belt getting worn, you don't want it to break. if you don't get fire from spark plug then you may have a bad coil,distubutor,rotor or timing sensor. if you get no fuel, fuse blown, bad fuel pump relay or fuel pump it self. hope that help some ..good luck

The timing belt might have slipped if it did you could crank until the cows come home and it wont start, thats the first place I would look,since yo have fuel and spark.

2002 kia optima has no fire to the spark plugs
or spark plug connector