Sage 50 Accounting 2013 Issues

Hello,
 
I am a student that purchased my Sage50 book with the software. I have a notebook so it does not have a CD drive so I downloaded the version from your website onto my external hard-drive. I was able to use it for about 2-3 weeks, but about a week ago I tried opening the program to do class work but received an error stating it was no longer available. All of the information was still on the hard-drive but was not able to access it. 
 
When I tried repairing it, I received an error stating that the "G:/" drive was not available, but my hard-drive reads as my H:/ drive. When I tried uninstalling the program so I can re-install it, it tells me that it cannot install the program (even though I chose to uninstall) because of the G drive. I tried this a few times and even tried deleting all the information on my hard-drive to see if that would work. When I tried reinstalling from the website the Install Wizard starts to load but then gives me an error stating I need a certain Windows 7 to install, I have Windows 7 Utimate version, but I'm confused as to why it was able to download the first time but now it will not allow me to re-install or even uninstall/repair at all. 
 
Please assist me with this issue as I am getting further and further behind in my class work. Thank you.