I went to the Apple Store and began the Mavericks download, but when it was time to install it stated it could not install on my Hard Drive when I clicked on my hard drive it stated "used for time machine backups" which it isn't. I have no clue as to why I can't complete the install and was hoping that maybe someone might be able to assist. I apologize in advance I don't have any further information. On a side note I had no trouble upgrading to Mountain Lion and I have about 395.76 GB of space available and 8 GB of Ram. Please tell me what you might need from me to help me trouble shoot this problem. Many thanks for your help in advance.