My HP laptop wont turn on

Hello,
My hp laptop cannot turn on. It doesnt even turn on when i remove the battery and plug it directly to the mains supply. I tried unwiring it and pressing the turn on button for 30 seconds with the battery removed, but it doesnt work. It has happened before but previously when i tried to turn it on it did turn on but it turned off a few seconds later. when this happened i would let it charge, however i don,t think that now that is the problem since it has been directly plugged to the mains supply for over a day. please help