Can anyone help?
A friend has unlocked my C180 97 manually with the key and it won't start! Central locking works fine, red light comes on when locking, green light comes on when unlocking but when ignition is turned on both lights flash alternately.
Never had a problem previously until key was used in drivers door lock! Is there a problem with door lock? perhaps a sticking micro switch etc.?

 

Did your friend unlock the door with the metal key that comes with the electronic key? If you have the valet key, the plasic one with no battery, try starting the car with that key, if that doesnn't work disconnect the battery for 30 minutes from the ground side, This should reset the cars CPU and perhaps then it will start.

I have unlocked the doors with the "key" remember the "key" wond't start the engine, you need the valet key or the electronic key to do that. The metal key will only unlock the doors and trunk. At ;least that how mine work on my 99 C280.