Okay, assuming you meant to type won't light up, let's start with the basics.
#1. Is the power on to the building you are trying to use this in? Hey you'd be suprised...
#2. Have you checked to make sure the circuit breaker and / or GFCI for the circuit the router is on isn't tripped?
#3. Is it on a UPS? If so, is the UPS turned on and plugged in / charged?
#4. Have you tried a different transformer for your router? (The voltage and amperage should be clearly marked somewhere on that router and / or the transformer.)
If you eliminate the rest of these, then something internal to the router has gone kaput Get a new one.