Vista not finding home network after router switched on/off by user.

As the title says.

Its a Vaio laptop, running Vista Home premium (not sp1 yet just about to
install after factory reset). Wired network. Home lan connected to the
internet via speedtouch 510 4 port router. When the router is switched back
on it finds an unknown wired network which has limited function ( local
only, no internet).

In network and sharing center only the actual network shows up, not the
"unknown" one. Network discovery is set to on. Sometimes it has switched
itself off but switching back on does not detect the correct network.

In Network connections the correct LAN is shown and also the Wireless
Network Connection which is not connected and the modem is switched off (
vaio has on/off switch on case).

Pulling the network cable for a few seconds and reinserting solves the
problem.

Is there a setting I've missed?

Thanks.