Not Starting/Overheating problem

[Fullmetaljacket]

Hello all, A few months ago I bought my Camry from a friend who was moving away. It has 110k and is in good condition. About a month ago I bought a house 120 miles away. My wife was driving the car back and forth to my old neighborhood for work purposes. My problem starts after a long period of driving on the highway with the A/C on the car gradually start to overheat.

I noticed the Camry takes much longer to overheat with the A/C off. Turning on the heater has little or no effect. It only overheats at highway speeds. I have checked the following:
(1) No visual coolant leaks detected
(2) Installed new thermostat (originally not present)
(3) Radiator & A/C fans work (always on with key in on position, will diagnose later)
(4) Radiator and reservoir are initially filled

It gets worse.... Overheating of course causes water to expand and displace from the radiator. I can usually make a full trip of 240 miles before refilling it. About a week ago I forgot the radiator cap off my wife was driving to work. According to her the car overheated and shut off at 70MPH after 15 minutes of driving. Now it doesn't start and the turnover sounds very strange like there is no load on the starter or when you take out all the spark plugs. I have done the following visual inspections sequentially:

(1) Starter solenoid - good
(2) Flywheel tooth broken or warn - good
(3) Timing belt - good
(4) DOHCs - good (spark plug boots were melted/fused to cylinder head, had to be torn/destroyed to remove valve cover.)

When the engine is turning over all corresponding parts appear to be turning camshafts, pulleys, belts etc., but it sounds like nothing in the engine is happening or the starter is spinning freely.

I know this post is long as hell, but it's all necessary. All brave souls help is appreciated.

[TTercel]

So no weird noises at all when you try and turn it over? Well since you checked spark, try checking compression and (not likely but still check) fuel. If none of those are the case, check your oil for any signs of coolant. You will know if there is coolant in there if your oil looks milky. If those arent the case id say you did some internal damage...

[Fullmetaljacket]

Your absolutely right I will do a compression test today or tomorrow. Could be a cracked head. The oil has no sign of coolant, but it may have all evaporated.