Start over. Run the Creative Suite Cleaner Tool, then try again. Also pending installs can come from otehr programs, not just Adobe software. Let them finish. If that's not possible, terminate all instances of setup.exe and msiexec.exe in your task manager before runing the Adobe install.
Thank you for your answer, but the Cleaner tool had nothing to clean and I have no pending instalations.
What else, please?
What is the exact error message you are receiving when you try to install? Have you tried running the Adobe Support Advisor - http://www.adobe.com/support/loganalyzer/ to automatically review your installation logs? Alternately you can follow the steps listed in Troubleshoot with install logs | CS5, CS5.5, CS6 - http://helpx.adobe.com/creative-suite/kb/troubleshoot-install-logs-cs5-cs5.html to manually review your installation logs.