If i were you I would reinstall dell support center. A new version may have came out. and for the sign in problem i recommend you uninstall ie9 and get ie8 or another browser
As far as getting the Windows Live Sign-in helper back, I would suggest you first try going to Control Panel-Programs and Features. Look for Windows Live Essentials and right click and select Repair. It should show up under Tools-Manage Add-ons-Toolbars and extensions.
If that doesn't work, unless someone know how to reinstate a BHO, I would think about reinstalling Windows Live.