This problem may possibly occurred if the device suffered wet or water damaged. The solution below shows the line paths of the SIM card pin connector to a particular circuit that might get faulty and result to nokia X5-01 insert sim card problem.
Nokia X5-01 SIM card connection line paths (SIM card ways)
In troubleshooting insert sim card problem you may first check and trace the SIM card pin connector connection such as the SIM card supply voltage and ground pin. IF these line paths were both okay, you may then consider that the problem lies on a faulty power management IC.
By reworking it might fix and repair the Nokia X5-01 insert sim card problem issue.