so it cranks but wont start?

an engine requires 3 things to run: air, fuel, and spark. once the starter spins and all those components are there it will run.

so if its cranking then you have an issue with one of the above. obviously there is air getting to the engine, so now check for spark. either get a spark tester or wear some insulated gloves, ground the plug and look to see if there is spark. is there spark? if no then its either your plugs, wires, coil pack, or ecu/sensors and all you can do there is test and replace stuff till you find out what it is.

if there is spark then obviously there is no fuel. pop out the injectors, make sure the wires to the injectors are intact, check your fuel lines, ensure the filter isnt clogged and the pump is operating. if those are all fine then its another sensor/ecu issue in which case you need to check resistance to all the sensors and inspect the ecu.

if all else fails, then give her a compression test, if you've lost enough compression you wont get the combustion in the cylinder and the engine wont run.

hope i've helped...