Vista - Strange problem with sony vaio vgn-n130g

I have a really annoying problem with my new sony vaio vgn-n130g that has
been occuring since i have upgraded to vista from XP (2 weeks back). the
vista installation somehow screwed up my bios setting (i think) and now the
monitor goes very dim as soon as i plug in ac power. everything works fine on
battery power. this behavior happens while booting also so i guess the
problem is not with display / power management drivers. i even installed
ubuntu linux and even then i had the same issues. now i am back on vista and
the computer is unusable while plugged in. i would appreciate any
help/guidance in this matter. the computer has a phoenix award bios which
does not allow me to change any settings apart from a very few.