tvonics DTR-Z500 digital tv recorder continually"starting up, please wait"?

the above will only play the station for less than a minute before reverting to "the recorder is starting up,please wait." the library is full, but it will not delete any programmes as it justs reverts to "starting up" again.
I have tried going to standby and switching off and unplugging for a while before switching on again, butit makes no difference.
Any ideas how to fix this?