Have you tried deleting the cache file? Here are the instructions for doing this if you have not done so already:
common_installation_issues.pdf
Please give this a try and if it does not work then there may be a corruption of your configuration folder. If this is the case you will need to rename the folder to get things working. Here is a link to the steps to take for this:
showpost.php?p=12293&postcount=2
If the issue persists let us know.