Lost recordings on Humax PVR9200T?

Every so often my Humax PVR9200T starts "misbehaving" i.e. press a function button and it's ages before it does it, if at all, or box freezes, and the only way out is to power it down. I switch off at rear of box first, wait a few seconds then switch off at socket. I give it five or ten minutes, then power back up in reverse order, after which it works fine (until the next time!) However more often than not I lose my recorded programmes off the hard drive. What am I doing wrong, and is there a way to get the recordings back if it does happen?