Ford Taurus not starting?

I have a 2003 ford Taurus, Thursday I drove to school then home no problem but when I went to pick up my son my car wouldn't start. I had power for the radio and a/c so I don't think it could be the battery. It just won't turn on for the pSt few days. Anyone know what could be wrong?

If yours has a panel dimming thumb wheel on the left of the dash, make sure it is not getting bumped toward full turn when you get in and out. This can run the battery down.
Secondly, the connections at the battery must be cleaned to a shine and tight at assembly.
The connection at the starter solenoid is an area of trouble for the b+ cable.
A test light can prove there's power, but does it actually make good contact with the solenoid stud? A second and third test here can prove this out.
arcing can be happenning, the resistance is there because of the fit of the parts, the arc disguises the fact the problem exists, the dirt and grime below can contaminate between the parts. The arcing can lead to an insulated condition.
The starter can also just need replaced because of its age and is suffering from multiple failures.
1 connections.both ends of both cables
2 solenoid loose.
3 starter bench test.
4 drains on the battery.
5 weak or not functioning alternator
6 unforseen trouble due to other previous work
and age of vehicle and its parts and of course your battery must be able to pass its tests.

Battery may be fine, but I bet the end of the wire that hooks to your battery is not making a good connection. There are two wires that hook to the battery, either on top or on the side. Check them!

The battery can still be strong enough to power the radio and lights but not strong enough to power the starter (largest load on the electrical system) start by having that tested.