Replaced battery now car won,t start.starter seems to grab but won,t turn engine over.seems like something is stuck? could it be starter? what about seized compressor. anyway to diagnose myself? please help.

Have you checked for correct fuel pressure? Most parts stores have a loan-a-tool fuel pressure gauge kit, and if you remove the plastic engine cover you will find a fuel rail port to attach the tester. Just because you replaced with new pump, don't assume it is good. Many cheap aftermarket pumps are noisy and fail often.

If pressure is good, insure you have spark to the plugs.

Open hood and look at left side of engine compartment. Find the braid jumper going from engine block to fender. Grab hold and wiggle. It may be loose from corrosion at the fender end. If possible tighten. If not replace with a new heavy jumper from block to body of car. This a major design flaw since battery charging current and starter current is forced through this skimpy wire and connection. I replaced battery and alternator twice before discovering this defect.

If the starter motor is turning the problem may be a broken flywheel tooth. If starter is not engaging the solenoid may be bad or not hooked up but that seems unlikely since starter was replaced. The problem's down there. If solenoid not clicking then problem may be further back.

Do you get warning lights on the dash ?
If yes, a mechanic would check for voltage at the starter.
The circuit between the key switch and the starter has a neutral or clutch safety switch that could have failed.

the clicking that you hear is coming from the starter relay. sounds like your ignition starter switch or ignition lock cylinder is bad.

Grab a test light go down to the starter, hook to a good ground and probe the battery cable. If that has power probe the solenoid engage wire( its the little one) have a helper turn the key to start if that gets power replace the starter.

The voltmeter should only go as high as 14-15 volts when the engine is running. I would check for a poor connection between the battery and starter.

If the car doesn't start with a jump you might have a bad alternator. The alternator supplies voltage to the car once the engine is running. If the battery is dead, and the alternator isn't putting out sufficient voltage, the engine cannot run. Then again sometimes a car with an extremely dead or internally shorted battery WON'T start with a jump. Replace the battery and try again.

Check the starter and the starter connections. freyed\loose connections...

(especially any grounds at the starter or any large common grounds)

There is most likely a problem with your starter -- if it is not grabbing the engine to turn it over when you turn the key, the starter motor will spin (giving you the whirring noise) but the engine will not move. First things first ... have someone turn the key, and hit your starter with a stick or something ... sometimes this will free up whatever part is not working proper5ly, and you won't have to replace your whole starter. If hitting your starter doesn't work ... and if you are good with cars, try replacing the starter and see if that helps.
Hopefully those will help ... if not, you will probably have to take the car to a mechanic to get it fixed, as there are several other parts that could be causing the issue -- but they are hard to get to and require some experience to know what you are looking for.