I had this problem, unfortunately. Here's how I solved it....
Go to System Properties (Windows Key + Pause Key)
Click the Hardware Tab
Click on Device Manager
Expand the DVD/CD-ROM Drives List
There should be two listed there - one of which does nothing as far as I can see
Disable one of them, restart, re-install, and see if it works
If not, disable the other one, restart, re-install.
Failing that, try re-lettering the drives
Also, if you download Sam's exe, I think you don't need the CD anyhow...