98 C230 wont crank or start

Does your dash light have any security light flashing? Have you recently changed keys? or added a battery to the keys?

Try turning the wheel to free the possible tension against the mechanism. try both directions and select park or neutral. apply the service brake, not the parking brake...... Does the key turn ? ....

Are your fuses and relays ok?

How old is the battery? That is a common Mercedes problem.

It is possible for a battery to be sulfated (losing usable space within) "capacity" at 4 years. That can reduce capacity it must be rated for and still posess. A battery rated better than enough has always been the answer when I have serviced Merc's. They usually have just one or two that would work in the merc's that i have fixed or done research for. This means selecting a very good brand and warranty is a must