Did you receive any error messages while trying to install? Which operating system are you using? I would recommend you start by running the Adobe Support Advisor - http://www.adobe.com/support/loganalyzer/ you can use this to automatically review your installation logs and attempt to locate a solution.
Thanks for contacting me. OS is snow leopard and the application is photoshop CS5 extended. When I try to open the application it asks me to reload software because some information is missing.
I have just uninstalled it and reinstalled it again, clearing all old photoshop products such as elements etc. I have never had trial versions of any Adobe products on my macs I have lightroom 3 elements and CS3. Fingers crossed this time.