I recently experienced a problem with my Talktalk TV box where new recordings would fail, and existing recordings would show only a black screen with no sound.
I tried various solutions to no avail - the remaining option being a full factory reset. This was not a great solution since one TV series (which we were half-way through) was not on catch-up. Long story short, this is what I did to recover my recordings:
The hard disc has a file system called XFS which is not supported by Windows, so I set up my PC to boot to Ubuntu Linux and provide the platform for the recovery. This is free and surprisingly easy to do as long as you have a spare hard disc on which to install Linux.
Next, I disconnected the cables to the hard disc in the Talktalk TV box, and used SATA connectors (data and power) to connect the disc to my PC. From within Linux, the drive was visible, but could not be accessed, presumably due to corruption.
Before starting the recovery, I "unmounted" the drive (this is an eject symbol in Ubuntu's file manager). From a command prompt I then entered the following command, where sdXX is the name of the drive as displayed in the Linux file manager:
sudo xfs_repair -L /dev/sdXX
Initially I got an error message to say that xfs_repair was not installed, however instructions were provided on how to do the install.
That's it, other than putting it all back together again.
WARNING: Taking the box apart may invalidate your guarantee. This is the solution of last resort.