how can I fix my fender pro 400 bass amp?

last time I used my amp, it worked fine . Now I get nothing. All the lights come on, all fuses are good, yet the speaker outs don't send a signal. Here's the confusing part, the head doesn't power the speakers in the cab and an external power amp won't power the the speakers either. And the cab head doesn't power an external speaker. Any advice would be helpful, thanks.