Windows 7: Problem: Laptop automatically powers on when plugged

I am having this problem for past a week.as soon as the charger is plugged into the laptop, the laptop gets automatically turn on (without pressing the power button). The laptop fully boot and not geving any other problem.
A laptop should turn on only when the power button is pressed. What makes the power bypass the power button and turn on? i don't know why this stupid laptop behaving like this i am very frustrated now because when i plugged it in it gets boot and i have to manually shuts it down every time.
please help me.

cmon guys plz some one help me. or tell me what i am doing wrong.

This is apparently a BIOS problem. Perhaps changing your CMOS battery and resetting the BIOS to default shall cure this problem.

can you plz tell me how can i reset BIOS?

Have you taken the Laptop to the vendor for getting the CMOS battery changed? When you do that he should also reset the BIOS for you.

However if you are determined to do it yourself then read at How To Clear CMOS (Reset BIOS). But resetting of BIOS should normally be done only after changing the CMOS battery.