Eskimomyworld, it definitely sounds like the battery is bad. Most new batteries only last 3 to 4 years. Remove and install a new battery or try charging your existing one. Most auto parts stores will test/charge batteries for free. Afterwards, check the alternator with a multimeter:
https://www.askmehelpdesk.com/cars-t...ml#post1973613
Jumping the battery is very dangerous--a voltage spike can fry the ECM, alternator, or sensors. Very expensive to fix. Best to just remove and fully charge/replace the battery.
On Tauruses, the starter is located between the radiator and the engine block, slightly on the driver's side. It's held on by two bolts. Remember to remove the negative battery cable first. On DOHC engines (Duratec), you may want to remove the battery and battery tray. Taurus starters are very good and last a long time--that is definitely not your problem.
The link below should help:
https://www.askmehelpdesk.com/cars-t...tml#post235560
FYI, there are 15 articles in the Ford and Mercury section of the "Sticky" that are directly applicable to your Taurus.