I don't have the Tyros, but this type of problem isn't isolated to a Tyros. It can happen to any keyboard that has a hard-drived installed. You're lucky the Tyros has an option of using the HD... I once owned a synth that relied solely on the HD.., Alesis Fusion 6HD.., what a nightmare) That synths HD coldn't even load its own voice engine at boot up.

I suspect you have a bad file.... It can be hard to locate the problem file at times. If you haven't done a hard reset of your Tyros yet.., def do that! What I would do is disconnect the HD.., then do a full system reset on your Tyros. See how she runs..., then hook that HD back up and go from there. If the problem comes back after connecting the HD back.., then you most likely have a bad file on the HD.