How do I reset the network adapter using a terminal command?

If you really want to reset the network adapter you usually need to unload and reload the kernel module that it uses.

If you just want to reconfigure it you can usually do:

sudo /etc/init.d/network-manager restart

But if you just want a new dhcp lease (that's the technical name for obtain a new IP from the router), you just need to use:

sudo dhclient -v eth1

This sound like a network-manager problem to me.

I would try the following: (in a gnome-terminal)

1. 'Softblock' your wireless device with rfkill block wifi
2. rfkill list will show you if you were successful.
3. killall nm-applet You kill the network-manager process (panel icon will be gone).
4. rfkill unblock wifi Enable wifi again.
5. nm-applet Load a new network-manager session.

Maybe simply killing/loading nm-applet will do. Also note, that you don't need to use 'sudo' for this.

I do know that some router and wifi devices do not 'like' each other very well. This is often a problem of a somehow 'beta' wifi linux-driver...