Left 4 dead 2 crash help?

Hey, I played left 4 dead 2 on my desktop and it worked but my lab top has a better graphics card. So I try it on my labtop and when the loading screen pops up for a mission It crashes. A black screen comes up with lagging sounds and nothing comes up. I dont understand how this is possible that a desktop with much worse graphics card beats my labtop that has a better one. They both have steam on them , and same exact installation. please help me..my graphics card are all updated..please help me...just tell me what I need to do..My desktop has windows xp while my labtop has win 7.