1995 Mustand V6 won't starts

I have 95 Mustang, V6, 250,000 miles.
When I try to start, it cranks fine, but engine won't start.
It used to crank for 4~5 sec before this happened.

Please help...

Pull a spark plug and install it in the plug wire. Using insulated pliers ground it against the block do you have spark.
If you have spark spray starting fluid into the intake and check if it will start.
After this is done repost results and I can tell you which way to go.