lan problem with sl500

[senbros]

hi guys
i'm susing windows vista ultimate with sl500. I 'm having problem connecting with lan when it is connected with ac adaptor. When i connect with battery..it get connected easily without any problem.
As soon as i pluged in ac.. gets diconnected. i'm using latest driver as provided by lenovo...and i'm using linksys router( cable and router works normally with other pc,, tested)

any help g8ly appreciated

thanks you