my 2000 mercury cougar wont start it has 100000 miles

One way to eliminate half of the possible problems is to spray a small amount of starting fluid into intake as you crank engine over. If the engine fires you now can focus on fuel system. If it doesn't fire look to ignition system.

turn on the ignition first and check for fuel preasure on the fuel rail there is a cap that looks like a tire cap take it off and depress the shrader valve you should have lots of presure and lots of fuel if not i suspect your fuel pump