If your router is not performing properly (freezing, automatically rebooting, disconnecting…etc.), this could be happening for a number of reasons.

Please check the following:
1. Ensure the router is in a well ventilated area. If the router does not get adequate airflow, it could overheat.
2. Ensure the firmware is up to date.
Firmware is the "brain" of the router, it is the programming that tells it how to work. D-Link will release new firmware versions when bugs are reported and fixed. Upgrading the firmware may correct issues you are experiencing.
Please follow this link for instructions of how to upgrade the firmware- How to upgrade firmware for router?
3. Perform a factory reset on the router. Please follow this link for instructions: Reset your router to factory default setting?