How are you trying to install and with what type of software? If you downloaded, you might have a bad copy or if you burned it, there may have been a bad burn.
Once you get the original problem fixed:
You can do a basic "clean" install if you use the custom install and tell it which partition to install on. The prior OS will not be used, but your data will be preserved and files on the new install. If you try wiping the drive first, you may invalidate any upgrade software and have to start over.