There's lots of things it could be, unfortunately. Do you have an nvidia or ATI radeon video card? If you have a radeon card, you should get the new Uru patch and try again.
Have you gotten Directx 9?
Upgraded your card drivers?
Have you tried reducing the graphics &/or sund settings or windowing it in the tabs at teh creation screen? That has helped some folks/.
If those ideas arent helpful there's a lively forum for Uru tech support on ubisoft.com that should be able to make further suggestions.
Me, I am going to have to upgrade my video card. A tnt2 nvidia 32MB card lacks some critical function or other so my copy wont play properly. The avatar creation screen comes up but my character is only shifting about in silhouette & then Uru crashes to desktop when it tries to load. oh well. One of these days...
May your difficulties be resolved soon!