You must install the Nokia Connectivity Cable Drivers to ensure your PC recognizes the phone via USB.
Older stable versions can be found in archives like Firmware Center . Nokia 6303i classic (RM-638): skachat proshivku na nokia 6303
A compatible micro-USB data cable and a fully charged battery. Installation Process Overview Nokia 6303 RM-443 V10.12 - Frendx.com You must install the Nokia Connectivity Cable Drivers