Most are easy to access. A volt meter or test light will help. Check for loose connections, verify power is at fan motor with switch or switches on. If there is power at motor leads, motor is bad. No power at motor then test backwards till you find power. Could be a bad switch or connection.
It depends on the fan you have. My original Ventline fan motor conked out in the first year or so. I replaced the motor and it's been working, but I want to replace with something different at some point.