Quick Fix: This is usually caused by overheating. Many of us
leave our routers running 24/7. As it ages, the router can become more
inefficient at cooling. Check to ensure the cooling vents on the router
are not obstructed. Unplug the router for a bit. Use a can of compressed
air to clear out as much dust as you can from the vents.
Newer routers have energy efficient settings that let you specify when it should shut the wireless radio off or power down, such as after 30 minutes of being idle. If your router doesn’t have this feature, best practice is to turn it off when it’s not being used to extend its life.
Internet Connection Tips; The Router Shuts Itself Off