If your battery is up and the battery connections are tight and not corroded then it's most likely your starter or your starters solenoid.
The Solenoid for the Ford Taurus is located on the starter itself so you will need to replace the solenoid on the starter or just replace the whole starter and solenoid which is recommended since the starter will have to come off.
Replacing the Solenoid can be done without replacing the starter but since the starter will have to be removed anyway you might has well replace the starter with a new starter which should come with a new solenoid mounted on the starter.