🚀 go-pugleaf

My problem is simple. When my PC is plugged into the phone line the
phone doesn't ring. I have checked a number of things:

I tried an alternate modem.
I tried an alternate PC, same problem
I tried at somebody else's house, ie a different phone line
I have checked the REN's. Pc is REN 1 and if phone is plugged in
instead it rings happily.
The PC is not set to receive faxes.
The PC does not answer the call.
The modem speaker does click upon an incoming call and light on an
external modem did go on and off.

Help, I keep forgetting to unplug the machine and miss telephone
calls.

TIA