I am running on windows 7, intel i3. HELP!!
I am not familiar with an ex20 error. I would recommend beginning by reviewing your installation logs for the exact error message. You can find details on how to locate and interpret your installation log at Troubleshoot with install logs | CS5, CS5.5, CS6 - http://helpx.adobe.com/creative-suite/kb/troubleshoot-install-logs-cs5 -cs5.html.
Exit code 20 occurs mainly due to permissions issue. You would receive this error if you are in a Corporate network where you will not have enough permissions OR you may have not logged on as an Admin.