You will have to order a new key from a Maserati dealer. They will require proof of ownership and identity.
When you get the new key, you will need to get it coded to the car to enable it to start. This needs to be done by a dealer.
To get it to open the doors, you usually need a working key!
In your situation I'd try:
1) New batteries in your existing key: *And make sure you don't lose that little piece of black plastic inside* It's the RIF transponder the car interrogates when you try to start.
2) Double press the lock / unlock button nice and close to the car. If they car and key have lost sequence, this will get them back in step.
3) Take it apart (carefully), and look at the buttons / switches on the circuit. Sometimes the rubber buttons fail to press the switches. Sometimes the switches break. All can be repaired.
If that gets you remotely opening / closing the door you can code a new key to do the same thing (but you'll still need to get a dealer to make the new key start the car)
No idea how you can make a new key lock and unlock without a working one. Maybe a dealer can do this as well, but they didn't when I got a new one.
C