What OS and hardware?
1) Does your system meet min requirements?
2) Did you install with the recommended settings? (admin account, anti-virus off, UAC off, nothing else running, etc.)
3) Download or physical version? If it's a download have you checked it's integrity (I think there's a MD5 check code with the download)? Or re-download just in case your present version is corrupt.
4) windows and drivers up to date (long shot, but worth trying if you've ruled out other options)