2006
 

So I went out to leave for work one morning and my 06 Freestar wouldn't start. It just clicked. I thought maybe the starter was locked up, so I tried hitting it, and still nothing. I tried switching batteries, nothing. Fast forward a week or so now nothing is happening and the keyless entry won't even work. Any ideas?

Welcome to the site..

Any lighting, instrument panel, heads etc?
Dim, or nothing?
Checked all the battery connections, pos/neg at the batt source and their connections?

Nothing is working. Did not check the cables down to their connectors.

Could there be a relay or sensor that could make this happen?

When nothing works, or has limited/reduced or no voltage, battery of course comes to mind, but if you changed it out, or had it tested and it passed, then the next step would be to check the connections both at the battery and the starter, as well as ground lug (trans bell housing area) for clean and tight since their subjected to heat/stress and corrosion. The Bussed/Fused Center has a direct feed input off of the battery POS, you might check the smaller distribution cable that attaches to the BEC under the plastic cover.. The BEC is between the battery and the left fender.

If all the cables have been checked, both ends to make sure it's not a power distribution or ground drop out, and If there's battery voltage 12.6-8 or so at the battery, and again tested at the BEC panel connector, spot check some of the fuses especially #64 and 67 since there input voltage for the ignition switch.