2001 ml320 will not start, start error is on dash, it turn over a couple times and then stop it will not turn again until i remove the battery cable from battery for 20 second reattach and the engine will turn over a couple more times and stop.

Where did you buy the alternator? Charge the battery and have them both tested.

try hold up the key while starting, shot in the dark. if it startes remove extra items off key ring

Check your alternator by starting engine and removing negative battery cable while running. If engine stops, replace alternator.

Never rinse the battery terminals or squirt water in the engine area of your car. If you get certain parts in the engine wet, the car cannot run. You might have wet something electrical that may work correctly again once it dries out completely.

Get a wire brush and pliers or a screw driver (depending on the type of battery terminal connections you have on your car) to remove all of the debris/corrosion on the posts correctly. Use the pliers or the screw driver to loosen the posts so you can remove them (one at a time). Life the post off of the battery & use the wire brush to remove everything on the post itself on top of the battery to the connector that is attached to the battery cable. Brush until you see a nice, clean metal connection free of rusty dust or corrosion. Reattach the battery cable and repeat the process on the other terminal. Once the terminals & connections are clean, you will need to jump start your battery in order to get the car to start again. Find a pair of battery cables & have a friend bring their car and park it as close to your engine as possible. Have them leave their car running. Open their hood and put the jumper cables on each terminal on their battery. Make sure you put the right color cable on the right terminal. then connect the other side of the jumper cables to the battery in your car. Have your friend press their gas pedal a couple of times to rev their engine, then try to start your car. continue until your car starts. then wait a few minutes to make sure your car battery gets enough of a charge to stay running. Leave your car running and disconnect the jumper cables. Driver your car around for a fifteen to twenty minutes to recharge the batter fully. If not, when you turn it off it will be dead again and it wont start.
If the car starts and the battery stays charged then your problem is solved. If you cannot get the car to turn over or hold a charge you might need to replace your alternator.

Good luck!

Sounds like the anti theft system is engaged.

Sounds like you have a loose connection on a battery cable. loosen the bolt and pull off each end and clean, then replace. When you clean them, make sure you get down to clean metal.

Have your alternator checked. Most auto supply places do this at no charge. Multiple dashboard warning lights usually indicate alternator problems.

sounds like your alarm is preventing the car from starting.

you can disconnect your negative battery cable, and wait about 10 minutes. put the key in the ignition and turn it to the ON position, but NOT to the START position. reconnet the battery cable CAREFULLY with the key ON, and the driver's side door OPEN. your alarm should "chirp" a few times, while reconnecting the battery. afterwards, try to start the car when the battery is tightly connected.

if the car still refuses to start, use the "panic" feature on your remote, to intentionally set off your alarm, and then turn it back off, to make sure it stops properly.

if this does not work, remove the fuse for your alarm, and try to start the car again without the fuse in place.....otherwise replace the fise and remove the pwoer connector from your alarm.

your actual alarm should be behind the trim plate, on the bottom side of your dash, above your gas and brake pedals....then try to start the car AGAIN....

if none of this works, then your alarm is defective and needs to be serviced be the installer, or manufacturer. also, calling the manufacturer will help too, as they have "reset and disable" features that can literally "bypass" your alarm.

seems like your key is not being recognized, possible your tumbler..the ring around your ignition switch is bad

this is one way to reset it :
first make sure the battery is fully charged , then do the following:
key in the ignition but do not crank the motor, just leave it at the
ignition mode for ten minutes ,then turn it off POSITION for 5 seconds then REPEAT again 2 more times. at the 3 rd time youre gonna notice the ANTI THEFT light on dash to blink. when doing the last step , remove key , inserted again and turn on motor , good luck , AJ