This is a "DAS" failure - Drive Authorization System.

The key has a chip inside that communicates with the EIS (switch module). There is a passive RFID chip in the key nose but also there is an IR handshake that happens.

First things first, make sure you are getting proper voltage to the electronics - does the mileage indicate on the display when you open the door?

Check key batteries as suggested earlier. Try just taking the batteries out, wiping them (like with a cloth?) and reseating them.

Did you happen to drop or damage your keys? I have heard of this happening, where the key gets dropped and the internal circuit board gets a crack in it. Or of course if the key gets dunked in water you're doomed.

The solution for this, if you only have the one key, and it's damaged, is a tow to the dealer.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech