Help with Microsoft Security Essentials on Windows 7 Pro

Try downloading a copy of Advanced System Care if you don't already have it, it will scan your system for registry errors and fix them. It also has a companion component from the same company (IOBIT) called uninstaller which will do a better job of getting rid of stuff. Or you can just download the Unistaller.

Both are available for free at IOBIT.COM. Read carefully when installing them as they will install other stuff you may not want unless you uncheck the boxes.