lock up?

I received this unit for Christmas. Used in numerous applications (children, nature sounds, personal music practice) at various sound levels, including external mic. I was quite pleased with the interface and friendliness.

It locked up, with most buttons inexplicably useless. It will continue to record/play, but without access to previous files or menu changes. I have tried taking batteries out and resetting as per the factory manual without success.

If this is an inherent design flaw, it'd be nice to know it. Naturally the unit "tanked" after 90 days, so repairs are out-of-pocket, I would imagine.