"He's dead, Jim".
I am almost certain that your phone has a hardware problem. There's a small chance that its power supply has gone bad. If you have another power supply with the same voltage and connector, you could try swapping it out.
As a final test, try this: completely delete your phone off of your OBiTALK dashboard web page. Then, on the phone, key in ***8 and then 1 to factory reset it. After it resets, don't re-add it to the OBiTALK dashboard or do any other configuring of the phone. Just try calling the OBiTALK echo test number: **9 222 222 222 and see if the phone reboots. If it reboots, it is defective.