Some things to check. Are you using the power adapter that came with the router? Is the router running hot? Did anything change about the time it started rebooting such as a new device or new software? Is your firmware up to date? Do you have anything in the USB drive port(s) as they have been know to cause issues if to much power is drained? Do you have any pets that may be moving the cables? Are you using a UPS as it or the battery may be failing. If you checked all that, then time for some tests. Disconnect all if the USB and Ethernet wired devices and see if it happens again. Also may want to try different Ethernet cables. Try a different power plug that is on a different circut as something may be causing an electrical spike. Do not rule out one of your devices may be sending a signal that causes it to reboot especially Unix based devices.