Be super sure you read which disc you put in and what instructions/prompts come up, while you are installing software. I was applying for a job, chatting on a dating site, looking at Facebook, and trying to install Microsoft Office on my PC again since I didn't do it last time the SSD went out. I realized only after the PC restarted and the install/unload functions started up that I did not insert the Office disc to install Office, but instead was upgrading my operating system. Oops. Fortunately it was installed as an upgrade and I lost none of my files or other applications. Wheww.
Lesson learned.