Can you launch ADE at all, if you open it as a standalone program? If not, ADE is broken.
Try uninstall and reinstall, or installing the superior old version (see below).
Or is it just from browser or explorer of a file that it will not launch? If so, it is the file association that is broken.
.... got to rush now ... if that is the issue post back and I'll respond how to fix it later.
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Some people have found ADE trying to upgrade automatically.
It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run.
Probably best to say no if 2.0.x installation asks if you want to migrate your library.