You haven't given us any information to help you fix this. For example, had you ever booted backtrack on VMWare before? If so, had you ever tried startx before this? If this is just after installation, then the problem is probably a corrupted iso, and you'll need to get a new one. Before that though, check the forums. There was a way to check if your image was corrupted. If you had successfully booted into it before, then what did you do that time? And, if you were able to boot into X before, you may have accidentally reconfigured a file. Sometimes, you'll just have to re-install. However, a reboot might fix everything.