The most common cause for this problem is that fixer was applied to the film before the latent image was developed.
Either the developer was somehow bad (expired, contaminated or improperly mixed) or else the fixer and developer have been applied in the wrong order. (e.g. Fixer was accidentally used first.)
Fixer removes all undeveloped silver halide from the film, making it no longer light-sensitive and, thus, there is probably nothing you can do to save the film.
As a test of your chemistry, take a strip of film a couple inches long and dunk it into a cupful of developer. You can do this in the light. The film should turn black in a short amount of time. If it does not turn black or if it takes a long time to turn black, your developer is bad.
While you are at it, test your fixer, too. Do the same test. Use undeveloped film. Just dunk it in a cupful of fixer. It should turn almost totally clear within a couple-three minutes.
If either of these test do not produce the expected results you have bad chemicals. Throw them out and get new.
If both of these test work as expected then you have probably mixed up the chemicals and have applied fixer before the developer.
Don't feel bad. Almost EVERYBODY makes this mistake one time.
You get distracted or you mix up the containers. It is a common mistake.
The best preventative is to label your containers and always arrange your chems in order of use.
I always premix and temper my chems to the proper temperature then set them out in order, dev - stop - fix - hypo clear, before I start working.
I won't say that I have never made this mistake but, since I started laying things out in order and sticking to it, I haven't made this mistake in a long time.
It's a mistake you only make once and you swear you'll never do it again... until it happens again!
