Try to rename or delete the WebSetup folder and try again.
Please let us know if you're able to continue after trying the above
Redownload or resume
When you purchase Windows 8 an email with the download link and purchase details will be sent to your email address that you use to purchase/register your product, you can just access that email and use the download link in it to re-download it on your computer.
Below are the links that will help you download Windows 8.
Note: Please refer to option 4 in first link below and to download the correct version from second link and use the product key of windows 8.