I would recommend using process of elimination until you can access the Start Menu. You can do this by closing an application running, possibly in the system tray, and then accessing the Start Menu to see what happens.
If you still have problems, run Windows Task Manager using Ctrl-Shift-Esc and try eliminating processes that may be causing this conflict. I would not be surprised if you launched the computer in safe mode that this problem would go away. If you do this (hit F8 repeatedly by booting and choose Safe Mode), and the problem still happens, it could be a problem with the registry or with the Windows system files themselves.
However, it would be best to take things step by step in this instance. Try to close whatever programs are running which may be causing the problem. If you still cannot eliminate the problem that way, you may want to track down what programs are launching at startup. To do this go to Start -> Search -> msconfig
Click on the Startup tab and you can evaluate what programs are starting by default whenever the system boots. You can disable many programs safely to try to remedy the problem, but it should also be done with care. Once you have isolated the program causing the issue, you should start to look more into the application to find a solution from the developer.