One is you have hit a bug in v2.0.x. Try using the less buggy 1.7.2 instead (see below).
The other is that you have an ereader device plugged in with lots of books on it.
A new installation of ADE has the very irritating habit of completely searching such a device for books that have nothing to do with ADE,
and writing lots of extra information about them to the device that you don't want there.
This is a very slow process, and it gives no indication that it is happening.
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.