reinstalling Autocad 2013 LT after crash

I'm still trying to reinstall Autocad 13 LT onto my mac.

I reinstalled the full AutoCAD LT 2013 with all the folders from the back up drive and it won't open.  It told me there is already an Autocad LT2013 installed on the computer. If i try to open that it says uninstall and reinstall. I uninstalled. It's now telling me i need OSX 10.6.4 or later, and gives me no other option than to close the message. I have OSX 10.10.1.

I need help please.

ML