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may want to check this too:

/etc/NetworkManager/nm-system-settings.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=true

Check both of these, should be:

/etc/NetworkManager/nm-system-settings.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=true

do you have more than one user account for your windows system?

Try checking these, should be set as:

/etc/NetworkManager/nm-system-settings.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=true

The username and password its asking for should be the one on your windows system. If you dont have one setup already it should be under user accounts in your windows control panel

One thing you may want to check is the mixer for your sound card. Not sure were it would be on Ubuntu though (Kubuntu you can access by clicking on the speaker in the notification area). Anyway, most...

If the network manager isn't crashing check these, should be set as:

/etc/NetworkManager/nm-system-settings.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=true