What have you tried so far? Your laptop should easily handle Diablo III.

The first thing to do is to remove any hardware you added after purchase.

Secondly, ensure all the drivers are updated.

Thirdly, post your Diablo III graphics settings on the forum. I haven't played it yet but someone might be able to assist you with optimizing the settings for Diablo. Sometimes one incorrect setting can adversly effect your game.

Lastly, check the Diablo forums to see if your anti-virus software is conflicting with the game. I have heard of a few people having this issus.