If your router is not performing properly (freezing, automatically rebooting, disconnecting, slow wireless speeds, low wireless signal, etc.), this could be happening for a number of reasons. Please check the following:

• Ensure the router is in a well ventilated area. If the router does not get adequate airflow, it could overheat and cause performance degradation.
• 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.
• Perform a factory reset on the router.  

For wireless connectivity issues:

Note: An easy way to determine if the issue is with the router or with the wireless device is to see if the issue exists on multiple devices. If you internet is slow or is only dropping on one of multiple devices/computers, then the issue is probably not with the router. If the router is the cause, all devices connected will be affected.

• Check your environment. Limit the number of walls between the router and your wireless clients. Large appliances, microwaves, glass, fish tanks, mirrors, metal, steel, brick, concrete, etc. can greatly affect the range and wireless quality. 
• Placement of your router. Ensure the router is in a central location and in the open area. Do not put the router in an enclosed area like a closet, cabinet, bookshelf, or under a desk. There should be at least 3 feet of open space around the antennas. Remember that the 2.4GHz band will get better distance than 5GHz through walls. Also, do not place near electrical equipment such as fans, fluorescent lighting, and air conditioning units.
• Antenna positioning. When the antennas are straight up, your horizontal coverage will be better. If you move the antennas sideways (multi-story house for example), your vertical coverage will be better. Adjust the antennas to see if signal quality improves.
• Change the wireless channel on your router. You can download free apps to your mobile device to see the number of wireless networks in your area and see which channels are open. If you have a lot of neighbors around you with wireless networks, this can cause interference, especially in apartments and dorms. To change the channel on your router, log in using a web browser, go to Settings > Wireless. Disable Smart Connect and click Advanced Settings for each band. Select a channel from the Wi-Fi Channel drop-down menu. Click Save.

Video - Get the most out of your D-Link router