insufficient privileges to install itunes

I have been trying to install itunes for over a year. I have been getting a message just before the end on the install, stating " (ipod services)insufficient privileges to start system services" Have called tech support and after many hours came to no resolve. Told it will be turned over to Engineering, but haven't heard for over 2 months. I have tried to add a user with computer administrator, but that doesn't work either. Turned off anti-virus software, no good. Have ininstalled ALL itunes, apple and quicktime software before trying to install a new download of itunes, still no good. Any other suggestions. Been using my laptop with itunes, but would like to use the larger memory desktop computer.