When I'm disconnected, I lose all connectivity both to the internet and on the local lan, so pinging (for example) Google
will time out, but also pinging 192.168.1.1 (the router's lan ip address) will also time out
Start -> dev manager -> network adapter. Double click, open her up and then under "advanced", take a look at "Link Speed & Duplex".
If this is set to auto-negotiation, try re-setting it to 10 or 100mbps Full Duplex, re-start your computer.
It's the network driver that costs me hours of hunting & searching.
MOTHERBOARD : ASUS IPIBL-LB
Integrated LAN : Realtek 8111C 10/100/1000 Mb/s (Gigabit Ethernet)