The Yaesu FT-857D uses relays for a variety of functions. Sometimes the relays will get buildup between their contacts and the radio can start acting odd, or certain functions stop working. Most people go to the reset procedures, but there is another troubleshooting technique that might fix the problem without losing memories and settings - Relay Cleaning. The FT-857D has relay cleaning built-in, and can be accomplished is just a few minutes.
If the relay cleaning doesn't work for your problem, consider running one of the Factory Reset procedures.