iPhone Backups
On a W7 system the itunes folder for backups is
C:\Users\username\AppData\Roaming\Apple Computer\MobileSync
There are many ways your backup can become corrupt ....especially if you pull out the USB cable in the middle of a backup.
This causes many issues, in particular itunes seems to hang when the phone is connected.
If you wait long enough (5 minutes or longer) it may respond.
Also when selecting preferences if itunes hangs you probably have a corrupt backup.
What I did was to cut the backup folder and put it somewhere else (do not delete it in case you may need it )
The folder name is 1771366aa7632780e554aab7d78f95c80767dd64 in my case.
Once you have an empty backup folder and you plug in your iphone you can re-create a new backup. This will take a while depending on how data you have on the iphone....be patient!!!