My 1998 Hyundai Elantra will not start after running out of gas.When I put gas in it ,it would crank but it took a long time to start. I drove it 3 miles and it shut off. I cranked it and cranked it,but it would not start. The fuel pump is working and Ichecked for plug spark with a timing light.The light did fire.The car did not overheat but there was a check engine code for a cooling fan circuit problem. What else can I do to solve this problem?

No compression may mean the timing belt has broken or slipped.

The fact that you have indicated the knock is in a very specific area of the engine indicates to me that the knock is there while idling and with you listening with the hood open. Spark knock, the kind that is caused by using lower-than-recommended octane gasoline, usually only happens when the engine is under load, not at idle.
I think you have a mechanical problem - valves, lash adjusters, maybe the cam itself. Do a compression check. If you have valves not working properly or not closing properly, this should help you find the area to check for damage.

You may have pumped a tank of bad gas originally. It might have had water in it along with some other bad stuff. The knocking could have been the water - water will not compress like gasoline will.
I think I would take a sample of whats in the tank and examine it.
You may have to try flushing out the fuel system including the injectors.

Weak fuel pump will do this

Was the car ever over heated at any time.Some friends of mine brought a elantra last summer, Where that was happening,I told them not to buy the car, But they didn,t listen to me, When i look at the car before they went end brougt it i could see antifreeze on the hood liner Where it shut out of the rad.This is a Problem with most 4 cylinder cars that i have seen. If they were Ever over heated at any time. End most of the 4 cylinder cars are bad for (Blowin)Head gaskets,Keep a eye on your temp Gauge.If it is working (Properly)

This sounds like you have a bad cam sensor. This is a common issue on most cars, and the when the sensor goes out completely you will not be able to crank the car w/out replacing it. What you are experiencing is like a warning, letting you know that it needs to be replaced. The part can be picked up at any auto parts store, and you may save some money if you buy it on line. Installation is easy as well.

maybe you have an oil leak

This is a known problem with the REAR struts, but not the front. This repair under warranty will have to be decided by the DPSM (District Parts Service Manager) serving that dealership. Good Luck.

MY 1999 hyundai elantra shutoff on the interstate when i took it out of cruise control and put it in neutal and will crank but not start.

Replace voltage regulator.