help..ac adaptor or motherboard?

Well, my laptops ac adaptor was working odd, and i had to put it in a certain position to work, (only one small part that goes into the laptop itself-not a cord) one of the little pins fell out, and it wouldnt stay in so i would put it in then push the pieces together. (the cord and the little right angled plug that snap together)
That worked for about a day, but now isn't working at all. I heard it might be a problem with the motherborad but i'm not sure. Is there a way I can test this, and a way i can fix it?

I have a compaq presario 2100 (and it sucks..)
and i have a right angled ac adaptor. made up of 3 detachable pieces.