Most black dongles have a small internal LED. If the light is off, the port is dead or the dongle has suffered hardware damage.
Finding a replacement "Black Dongle" can be difficult because Wilcom has moved toward cloud-based licensing and newer dongle generations. Black Wilcom Embroidery Studio E2 Usb Dongle
You may find them on eBay or specialized embroidery forums, but be wary of "cracked" versions or clones that do not receive official support. Most black dongles have a small internal LED