Why does my screen blink black when I plug or unplug my charger?

Whenever I plug in the charger the screen blinks black for a second, but goes back to normal afterward, and lags the computer for a few seconds (i figured that because my music or videos skips on WMP). The same thing happens when I unplug the charger.  I didn't used to have this problem, it started happening when I reinstalled windows xp pro or updated to service package 2.  But the previous times when I reinstalled windows, it never gave me this problem.  The first time my brother reinstalled Windows he had this problem, and recently just reinstalled windows and he doesn't have this problem.  Also, we have the same exact laptop and we used the same Windows XP Pro. disc.

I don't know how to bring up all my information, I'm guessing its called BIOS, but I have a Dell Latitude D531, it has AMD Turion 64 X2 TL-56, 1gb of RAM, using SP2, using an OEM battery and charger(I highly doubt the battery and charger are the problem, but I thought I should mention that).

If you need anymore information I'm more than welcome to get it as long as you'll willing to tell me how to find it if I have trouble.

Any help will be well appreciated. Thanks