Usually a Laptop switches automatically to battery when AC disconnected.
What make/model of Laptop?
Allthough perhaps, assuming win boots when on AC, youve amended your WinXp
Power Settings in some way to only use AC
"sam" <(E-Mail Removed)> wrote in message
news

130763E-8A00-4C98-9E14-(E-Mail Removed)...
> I have a laptop and usually runs on battery with ac power as a backup and
to
> charge the battery. for the past 2 days my battery is showing 75-100%
power
> but i cannot either switch my pc on or alternatively, if on, when the ac
> power is removed the computer immediately shuts down. I have looked at the
> power supply icon but i don't know which one is to turn it back to battery
> power, please help.