I think most - if not all - preloaded extensions you enabled show up under different menus. And some extension require that you restart SU to load.
Your profile says you are using XP. You don’t mention how you are downloading. If yo are trying to download from inside SU, some of the downloading issues may be related to working with an older OS that only supports up to IE8.
Did you upgrade to SU14 from SU8 because it’s the latest version of SU you can run on XP - see Heads Up…?
Did you try clearing the cache and cookies on IE regarding the downloading problem?
Try navigating to the Extension Warehouse in a web browser of your choice and download extensions that way then manually install through Window > Preferences > Extensions?