nc 8430 modem problem

[Ljudevit Oresic]

Hi!
i've recently bought hp nc8430 and i'm very pleased with it, but i have run into a little problem. the problem is, when i try to connect to internet using modem when the computer is on battery it's all okay, but when i try to connect while plugged on AC power it can't connect or do anything. i tried connecting when on battery, then plugging in but as soon as i plug in it can't search the web or anything. the connection icon on taskbar shows that it is connected, but it doesn't work.
plz can u help me with this?
thx! :)