I've had a strange issue over the last few weeks where my modem (a <1 month old TP-Link 8960N) will be unable to negotiate a PPP connection - in the router system log it just loops the two following lines:

syslog: PPP: Start to connect ...
kernel: netdev path : pppoa0 -> atm0

over and over again.

Curiously enough, if I call the helpline (having gone through the normal troubleshooting steps including isolation tests and factory resetting the modem/checking login details/settings, using a different router) and have them request a port reset/refresh, the connection springs back into life and I'm able to connect again.  This would be great, however it seems that I lose the connection again when I restart my router...

Having called the helpline three times for a port refresh in the last month or so, I requested a Chorus callout - he plugged a DSE modem in and was able to get an authenticated PPP session running.  After speaking to someone on the phone, his conclusion was that it had to be a problem with my computer configuration, the router configuration or incorrect ISP login settings (all of which are clearly not the issue since the router isn't even getting to the authentication stage).  After a bit of haggling, they've agreed to switch me onto a different port.

...I'm now afraid to restart the modem in case I lose the connection again!

Has anyone had a similar experience?  I'd be willing to blame the modem, but it's practically brand new and my old modem (an older revision of the TP-Link 8960N with different hardware/firmware) has the same issue.