had the exact same problem try hitting the unlock on the remote key thing... then put the key in and turn it to on but dont start it. crank on the wheel really hard to one side while applieing the brake and start it. it works. it has to do with the alarm system
the battery could have a dead cell, this could cause it to not charge. Have the battery tested to be sure.
Its bad Clean the battery connections and make sure the connections are good. If the battery has been tested, has it been tested under an actual load, not just by placing the meter on it? also if the cells of the battery are beginning to break down, it will discharge at inopportune times,
Take a battery from each different battery type (prefferably three). Leave those out in the same conditions as the ones being tested when the one being tested is determined "dead", take a voltmeter and compare the control battery with the tested battery.
the sprag clutch is gone the sprag clutch is part of the small gear in the starter basically you need to buy a new gear or a new starter depending on the price it is often called the bendix
Have your battery tested first, if it is good most likely it is a bad alternator, have that tested as well
Presuming you've got and automatic gearbox: To be able to engage neutral there needs to be power from the battery. So either jump start the car or charge the battery, but you need to find out why the battery died in the first place. If you left lights on something like that then charge the battery by taking it for a long drive. If the battery goes flat again after that then there may be a problem with your alternator or the battery won't hold a charge, get the battery tested and go from there
On a 2000 Merc. it's usually an emissions problem. You can try a water dryer for the fuel and change the PCV valve. If the light remains on, then more than likely it's the EGR valve. Have it tested for free at autozone or Advance auto.
Have the battery tested at any auto parts store.
Start with having the battery tested then be sure the battery connections are clean and tight. Check the starter relay. Try moving the shift selector from park to neutral then back to park. If the starter still won't engage you may have a faulty starter.
Dead cell in the battery or something is on pulling power from the battery. Have the battery tested at any auto parts store.
Get your alternator tested at autozone,its free,and check your battery too.
Fully charge the battery and have it load tested at anyplace that sells batteries.