If the TP-SK706S-PC822 is critical and the firmware has not been updated in over 5 years, push for replacement. If the line is scheduled for decommissioning in 18 months, perform the firmware update.
If your TP-SK706S-PC822 no longer responds to touch or USB after a failed update, you have a "soft brick." To recover: Tp-sk706s-pc822 Firmware