low voltage to crank shaft pos. sensor

Well, the first thing to do; is to check and see, if your timing marks line up. If they do not; then, I would inspect the timing belt and see if it is damaged. Many times; the timing belt will get damaged, because something in the belt path has failed (water pump, pulleys, tensioner, etc.). You would want to fix those issues and then you could do a compression test. If the compression is zero; then, you have bent valves. At that point; the head would need to come off and it would need to be repaired or replaced. Put everything back together with a new timing belt/waterpump kit, head bolts, head gasket, (anything else you need) and then, you would be back on the road.

timing belt replacement and timing marks alignment:

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Maintenance > Timing Belt > Component Information > Service and Repair > Procedures

compression test; specs and procedure:

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Maintenance > Tune-up and Engine Performance Checks > Compression Check > System Information > Specifications

Here is a excellent thread; showing what is involved in replacing the head:

http://newbeetle.org/forums/2-0-liter-gas/25533-well-i-did.html

Well, as I said; you need to do some testing and checking to see what is wrong. If all the timing marks are correct, the timing belt isn't damaged and you have good compression, then the sensor may or may not be bad. You could also; check and see if you are getting spark, at your spark plugs. If you are not getting spark; then, the camshaft position sensor, could be bad or wiring is bad or the timing is off.

16726/P0342/000834 - Camshaft Position Sensor (G40): Signal Low

Possible Symptoms
Malfunction Indicator Light (MIL) active

Possible Causes
Wiring from/to Camshaft Position Sensor (G40) faulty
Camshaft Position Sensor (G40) faulty
Timing misaligned

Possible Solutions
Check Wiring from/to Camshaft Position Sensor (G40)
Check Camshaft Position Sensor (G40)
Check Timing

The P0135 Volkswagen - HO2S11 Sensor Heater Circuit issue; is unrelated to the "no start" problem. Part of the 02 sensor is bad; the "heater circuit", that problem would require a new 02 sensor to be fixed. I would deal with that; after you find out, why your car isn't starting.