There are two Sim card slot for the C1-00, so you may only check which one has a problem. If both SIM slot do have the trouble, you may first try to restore the device flash firmware.
To easily fix insert SIM card problem of Nokia C1-00, you may first check and clean the SIM card pin connector for possible damaged and oxidation build-ups.
Once the SIM card pin connectors already confirmed okay. You may refer to the solution below and do have some hardware check and test procedures.
Nokia C1-00 Insert SIM card Problem Solution
Connection Line Paths and Components Layout
The solution above shows the detailed info of the Nokia C1-00 SIM card connection.
You may use to trace each corresponding SIM card pins connection down to where it is being connected.
The layout also shows the solder ball bumps where the SIM data signals is feeds from the main power chip for deeper troubleshooting procedures for there is a tendency that you may also need to remove and rework the said IC, just to fix the Nokia C1-00 with Insert SIM Card Error Problem.