laptop battery not charging

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i'm having trouble getting my laptop battery to recharge. i unplugged it and used it for 30 minutes or so the other day, and after plugging it back in i noticed that when i hovered my mouse over the batter/plug icon on the taskbar it said "44% available, not charging".

is there something i have to do in windows vista's settings to get my battery to charge? i've tried shutting down, hibernating, and putting it in sleep mode... still won't charge.

help?