Desktop Screen doesn't appear

My desktop screen never opens up. The computer just keeps thinking about it. Apparently a program is trying to load. How do I find out what it is or get it to load. Everything else works fine. I can go on the internet from the start menu by clicking on that icon. When I use my scanner it reinstalls everytime. I tried to uninstall it and reload it with the disk I get an error saying another program is trying to install, try again later. I have a feeling maybe the scanner is the problem, but I don't know what program it is that is trying to install. Has anyone else had this problem?
Thanks

Hi Jeannie, I'm a little confused by what you mean with "My desktop screen never opens up"... does the start menu appear ok, but the icons on your desktop never appear?

Does Windows 7 work OK in safe mode (as this doesn't load most startup applications), and can be used to troubleshoot. To do this, perform the following steps: