Why wont this truck start?

OK.... a friend of mine owns a 1999 pick up truck... it's a small one, like a ford 150 or something... ne way, his truck wont start. when the ignition is turned..... u can hear the engine trying to start.... it's just not firing up. I thought it to be the starter, by the way he was explaining it.... but when i tested the truck my self....it is actually attempting to start.... it's turning.... but not firing up... it just goes " Err... gee gee gee gee gee"... bst way i can explain it.... all power works, so it's not the battery (tried a jump ne way, no luck)... the starter is doing it's job ... there is no grinding noise, so it can't be the fly wheel.... ne thing else???? oh and btw, he sys that he had a new fuel injector put into the truck already.... so it's not that either..... thanks we appreciate it