1995 Mercedes Benz C220 the engine key wont turn

first things first is to try another key if you had one. possible that key is very worn or bent causing issue. with it not turning, next is turn steering wheel off of wheel lock to remove tension from key cylinder if steering wheel lock is applied. if no issues noticed with this try spraying some graphite lock lubricant or equivalent thin lube in key cylinder and keep working key in and out and trying to turn it, once turned do not turn key fully off you will have to install a new lock cylinder, and you will need key to turn to replace.