I had to reinstall Mac OSX Lion after I lost some data. Now I miss some minor functions like right mouse click. I guess it has to do something with the system library. How can I correct that?
Ah. You did not say that you had already tried that.
When the changes do not stick, this may be because permissions make the property list file unavailable to be re-written with the new information.
There are two Library folders:
The first contains the system-wide preferences set by the original Administrator. Its permissions can be reset by using Disk Utility ( Repair Permissions ). [it is always prudent to perform a Disk Utility ( Repair Disk ) first. If not available, a ( Verify Disk ) will suffice as long as no repairs are needed.]
The second is your personal Library, which is located at /Users/your_user_name/Library but is often invisible by default. You can use the Finder's GO menu, choose Go To Folder, and enter: ~/Library/Preferences
The file that appears to hold these preferences is :
Opening that file may damage it. But you can GetInfo on the file and be sure that under Sharing&Permissions, Owner is your_user_name, and that Group:staff has permissions Read&Write