If you are asking about the current "tall" or "tower" shaped AirPort Extreme, the internal fan on this model tends to get clogged with dust after approximately a year of operation. As you might imagine, when the fan cannot move enough air to keep the internal power supply cool, the supply will start to overheat....yet the AirPort Extreme will not feel warmer if you put you hand on the device.
If the AirPort Extreme is less than a year old, Apple will replace the device for you at no charge.
If....the AirPort is more than a year old, but less than three.....AND...you have AppleCare in effect on one of your Macs, then the AirPort Extreme will likely be covered as well. Contact Apple Support for details.
If the AirPort is not covered at all, about all that you can do is manually open up the AirPort and clean out the fan, or replace the fan if needed. This article might provide a few tips on that operation:
https://www.ifixit.com/Teardown/AirPort+Extreme+A1521+Teardown/15044