Without further information, it is difficult to determine the exact reason why the user is unable to install the 2008 version of Scrapbooks Plus on their Dell Inspiron 3847. However, it could be due to compatibility issues between the software and the computer's operating system or hardware. It is recommended for the user to check the system requirements of the software and ensure that their computer meets those specifications. Additionally, contacting the software's support team or referring to the user manual may provide further assistance in troubleshooting the installation issue.