there are three thing that you need to make your radio work.

1 constant
2 accessory
3 ground

constant fuses will ususally be under the hood about a 10 or 15 amp fuse. another why to check to see if this works is if your dome light works.
usually
accessory fuses will be in the kick panel and is a 10 amp fuse.

ground just need to touch to metal of your car

if all else fails pull out each fuse one at a time and check them all. or buy a multimeter and pull out your radio and check your wires