The 1994 & later US model C-Class have a starter interlock relay!!
On cars without an alarm system the central locking system MUST send signal to this relay before the starter will engage.
If the car has a factory alarm then the signal cones from the alarm ECU.
Next time that this happens TRY locking & unlocking the car several times & then see if the starter will work.
ALSO the central locking system MUST work.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator