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.
North America
Europe, Middle East and Africa
Asia Pacific