Just for fun did you swap out power adapters? I would hold the reset button for 4-5 seconds. If resetting the device doesn't get you a blue-led it sounds like a hardware problem. There are some cheaper single M9 replacements on eBay than buying from retail.

@Mul 

Try moving the unit to be the base unit using that units power supply.  connect the previous base unit with the power supply of the one not working and see if the swap conditions.  If they do the the issue may either be simply the power cord or the outlet has gone bad.  If you relocate that unit and it works then the issue may very well be in the outlet a short perhaps.  If not and the issue persist, then its likely a bad unit and you can simply request a replacement as long as you bought the unit from an authorized retialer and its still in warranty.  

Avoid buying on eBay unless its from TP-Link's official storefronts or NewEgg's as everyone else is a 2nd hand product (regardless of stated condition) and not valid for warranties.