Hyundai Repair: 2001 hyundai sonata wont start, crank sensor, camshaft timing

Question
I have a 4 cylinder 2001 Hyundai sonata that I bought used 5 months ago. When I bought it it had a slight knocking while idling which got louder if the weather was cold. It ran fine no problems then I drove it home one night parked it then went to start it in the morning and it wouldn't start. It cranks and sounds like it wants to start but won't turn over. I even tried to see if it will start with ether. I tried many times after that but it still wouldn't start. I have changed the ingestion coils, checked the fuel lines, checked the battery. The only other thing I can think of is that it's not getting compression.Could that knocking been a valve? Or I've been hearing something about a crank sensor, could that be it? Please help. Thank you.  

Answer
The problem could be anything that would cause lack of fuel, lack of spark-- including but not limited to the crank sensor, or lack of compression.  

How does the engine crank?  

If it cranks fast, you'll want to check the camshaft timing.  If ok, then next do a compression test.

If it cranks at normal speed, you'll want to check to see whether you have spark and fuel pressure.

If it cranks slowly, you'll want to recheck the battery and voltage during cranking.

In either of the first two cases, it may be helpful to read the codes from the engine control module (ECM) if you have a way to do that.

If I had to guess, I'd suspect the knocking noise you heard was coming from the timing belt, and the timing belt has now failed.