If a starter is able to crank the engine but it won't start you usually have either an electrical or fuel problem. It's also remotely possibly that it's compression.If an engine has proper fuel, spark and compression, it will start when you crank it. So your challange is to find out which part isn't working right. Start with fuel. Spray a little starting fluid into the air intake while someone tries to start the engine. If it starts briefly when you're spraying starting fluid, you probably have a fuel delivery problem. That could be injectors, fuel pump, fuel filter, relay, fuse... who knows what until you check into it.If it doesn't start with starting fluid, check the spark. Pull a plug wire and attach it to a spare sparkplug and set the plug on a solid metal
part of the engine. Have a helper crank the engine while you watch the plug. If you have a good spark, it might just be out of timing.In any case, you'll need to start isolating the problem. Find out which part isn't working then you'll know what to replace/repair.