hi i really need some help on my laptop i have a acer 4820t. basically last week i was using it plugged in, and it just turned off. wouldnt start. wouldnt turn on without battery or with battery. tested the charger, it works. so was told i need a new motherboard. so i bought one of ebay, changed them over. laptop now starts up now, but theres no screen. the fan just gets really loud. the screen is not a problem as i have tried using a external screen and it doesnt work. thanks