A "rapidly blinking light" sounds like a hardware
issue to me, not an "open port." It sounds to me like your router might be failing!
The term "open port" means that:
- Some TCP/IP port can be connected-to from the outside, and ...
- Some program on your computer is actually waiting for a connection-request on that port. (Either directly or through xinetd.)
This term is a software
term. It does not specifically involve (router ...) hardware
P.S.: The "blinking lights" on a network device can be totally misleading. I once saw "blinking lights" on a box that was stone dead