Inspiron 9200 with internal card.

This has just started happening on my home network - when connected to power I can connect to the network but after 1-2 hours the connection disappears and I get the "no wireless networks found" in Wireless network connection.

Here is the rub - if I disconnect external power and hit refresh the computer reconnects (and sees all 3 wireless networks available in my living room.) If I leave the computer plugged into the wall then refresh does nothing...

I have tried disabling the etherner card but that didn't help.

The only things changed recently are installation of internal bluetooth card and a Windows update a couple of days ago.