If you see the same symptom after you connect a PC directly to the A100 and power cycle the box, then the software / firmware of the A100 is corrupted. The only thing you can do is to RMA the box.
If you can ping the box after you power cycle it, and you still can not see it on the GUI, you may want to perform an Emergency Recovery of the box. The procedures for Emergency Recovery can be found in Chapter 4: Hardware Installation of the Abacus 100 Analog Subscriber Generator Installation Guide.