2005 Mercury Sable Car wont turn over

I have a 2005 Merc Sable with 3.0 i replaced the battery a month ago seems to be fine over the last week it has sounded like the battery was low or dead when trying to start had it tested it is good when trying to start it would give the clicking and and slow turn over but would eventually start now even with a good battery it wont do anything when you turn the key to the start posistion but when trying to start it the starter relay under the hood is clicking just to be sure i did replace it still nothing already checked fuses any help would be apreciated