Have you tried deleting your cache file with the steps listed in this document?
common_installation_issues.pdf
Please give this a try, if you continue to have problems there might be an issue with your configuration folder. If this is the case you should be able to get past the issue by renaming your configuration folder, here is a link to instructions on this:
showpost.php?p=12293&postcount=2
Please post back and let us know if you continue to have problems with this.