You give absolutely no information in this post whatsoever for anybody to be able to help you.
0.) You've verified the MD5 sum first off correct?
1.) How are you running backtrack (LiveCD, HD install, USB, through vmware)
2.) Specs of your computer (type of video card, etc..)?
3.) Any error messages?
This type of information at the very minimum will be required. We are not mind readers here and in order for us to help you, you will need to help us by doing some research first.