Why I can't launch Adobe Digital Editions 2.0 on my Win7?

My ADE 2.0 used to work well. But when I tried to use it today, I did not open. I double-clicked many times, there was not response. I then uninstalled and reinstalled, no result. I installed 1.7, it can be opened, but forced me to install the latest version 2.0. When I installed 2.0 again, it did not open. What can I do?