Just to continue on the other track, the thing is if the software is talking about COM1 *and* COM2, there might be two ports configured even if there's only one physical serial port (ie. an infrared port, which would still count).

Also, what do you mean by "the strange thing is that my old RC5200 IS responding to the same PC with the same configuration"? Are you talking about the "replaced" RC5200 (I would assume from your original post that it was dead).

Something you can also try is applying pressure either up or down to the cable where it enters the remote. Sometimes if the port is just slightly "bad", doing this can help contact.

Also, look through the FAQ for how to communicate with the Pronto via Terminal, which will at least let you know if the problem is physical or software with ProntoEdit/the PC configuration.