Macintosh or Windows? What exact version of the OS?
Did you use the Adobe Uninstaller to uninstall the old installation first?
Never just drag the application to the trash. Always use the Adobe Uninstaller.
Search for, download and run the Adobe CSClean Script.
If on Mac, then repair permissions with Apple'sDisk Utility before and after every installation of an application or update of the OS.
More details would help.
Please read this FAQ for advice on how to ask your questions correctly for quicker and better answers:
Welcome to the forum.
Along with the questions that Station_Two posited, and those in the FAQ Entry, I have a few more questions:
Are you getting any error messages?
Is your installation disc damaged in any way?
Do you have adequate free-space on the destination HDD?
Along with those, this article covers some general Adobe installation points. Take a look, and see if you are following those: http://forums.adobe.com/message/3419692#3419692
Good luck, and please let us know more,