Single red blink on reset

A-Star 32U4 Mini SV. Was working fine until I tried to power it externally from an 18V power adapter.
Now it blinks red on restart and can not be programmed, no matter what’s the power source (external or usb).

I am sorry your usual method of programming is not working. Can you try following the instructions under the Reviving an unresponsive A-Star section of the A-Star’s user’s guide and see if that solves the problem?