2000 ml 320 turn key and wont start full power on battery all dash lights come on just wont crank but i can go under neath the car and jump it at the starter and it fires right up

Does the car push-start (or actually the engine crank turning)? If yes then it has to be a battery or starter solenoid/starter motor problem. In some cases it can be the power cable to the starter motor. Check the terminal connections to be clean, good and solid. First of all though check the voltage drop at your battery when the key turns to start. If the voltage drops under 10V then your battery is weak and you should try either jump starting or put another known good battery and test.

Check fuel pressure and also check for engine control fault codes

the starter uses 10x more elect. power than the head lamps
or 100x more than dash lamps. it means little.
what matters most is jumper cable starts.
does it crank with jumper cables to a running, donor car,(aaa jump)
no bad starter
no, bad starter key line( immobliizer or such) ask how to test.
yes, cranks great, now.
that means the battery was dead,
i charge the battery and it now cranks, due to lights left on or
charge system failure, if battery goes to 13.3 to 15v running good
if on the charge system failed. (causing battery discharge)
if after charging a battery it will not crank car, its a bad battery (jumps ok)

Did you check all the fuses under the hood? That's where the ignition fuses would be. The same "run" wire to the ignition coils, when the key is in on or run, or the same set of run wires out of the ignition switch both to the dash warning lights and gauges, and to the ignition system on the engine, well they're all the same power source, and more so the computer gets power from the ignition switch being on as exhibited by the check engine light turning on when key is turned to on.
It sounds like the ignition switch is either not getting full power in, or it's not sending power out as it should.
Check your other battery power-do you have headlights? That would be entirely separate from the ignition switch, but it verifies that battery power is getting to the fuse and relay block under the hood. Is the cranking speed normal? not too slow?

I had a similar problem with a 1999 Chevy Astro. All fuses checked out good. Several posts advised cleaning the battery terminals, checking out the ECU to cutting the yellow wire from the ignition switch, check to see if it'll crank on Neutral, and also checking/replacing the brake switch. I simply removed several keys from the key ring, then shot several bursts of air from an air can (some keys are keyed to the ECU to turn off the Security System when attempting to start the engine), then waited several minutes for any condensation to dissipate, then was able to crank the engine to life.

turn on head lights have some one try and start car if the lights do not go dim then the starter is not drawing any power take starter out replace or rebuild can take starer out and hook to the battery its a 98 should have put 3 or 4 starter in by now I have

If the headlights and dashboard lights are working but the vehicle still does not start, the ignition switch is most likely the problem. or a bad wire from switch. If your battery checks out, but the starter is still silent, it may be a faulty ignition switch. Turn the key to the on position (not all the way to start). If the red warning lights on your dash don't light up (and your battery connections are clean), the ignition switch is bad. If they do light up, turn the key to the start position. The dash warning lights should turn off at this key position (most cars). If you're not sure, turn on the headlights. When you try to start the car, the lights should either dim (a lot) or turn off completely. If they do, your ignition switch should be ok. If not, the switch will need replacement. check the wires to starter and see if you have power when car is switched on, do this first! good-day! if it cranks but does not start. check to see if spark and fuel, and check all fuses also.

One of 2 things. Either the battery is low, you have power, but not enough cranking amps to start car. Or the antitheft is not communicating correctly and the ticking sound is from the TDM . (theft deterrent module). Here is a link for the antitheft system. If you see a light on your dash that says "security" then this is your problem. http://vatspasslockpasskeysecurityhelp.yolasite.com/

Try replacing the negative and positive battery cables. Sounds like that could be your problem.

sounds like you need a new battery, it probably isnt running enought cranking amps to start your car, try a different battery and it should start fine