My car is not downshifting right from 3nd 2nd 1st?

I have a 1999 ford cobra 5 speed. when i downshift i can go down down to 4th but when i hit 3nd 2nd or even st. The car wont go in the gear the rpm goes down to 1000 like its in neutral or idling. I down shift when the rpms hit 1300-1500 Whats wrong is the clutch going bad or transmission or maybe im not downshifting right