For a .pdf of the user guide look
here, and for information on the current firmware
here.
Freezing is likely (if not a hardware fault) to be due to a combination of out-of-date firmware and receiving a particular channel.
To recover if the freezing always occurs within a few seconds of switching on or changing to a particular channel, power off the PVR, remove the aerial input, start up the PVR and perform a defaults setting (all user settings eg. aspect ratio, jump buttons, favourite channels, future recording timers will need resetting later after tuning in, but recordings on the HDD will be retained). Then power off, reconnect the aerial, restart and tune in. Manual tuning is the preferred method with Humax PVR9xx0 machines if there is any likelihood that channels from multiple regions/transmitters may be received - it is important to Freeview+ recordings that channels stored at the primary LCNs are from a common transmitter.