I would recommend that you reflash with the FULL 796 reflasher, as linked to here:
This will completely recreate the internal partition and restore all the system files. Back up your books and fonts from the internal partition first - you'll lose them in the process.
It sounds as though you may have inadvertently unplugged the Gen3 from your PC without properly dismounting it - this can easily lead to disk corruption. ALWAYS use the "Safely Remove Hardware" tool before unplugging the USB cable.