When you see "apc ups power system error 02000 link," do the following in order. UPS units contain high voltage even when unplugged.
If you have reseated the hardware and updated the firmware but the error persists, the internal communication board (interface board) may be physically damaged. Contact APC Support (Schneider Electric) and provide them with the specific error code (02000) and the serial number of the unit. apc ups power system error 02000 link