Microsoft Security Essentials - no menu item to open it

I'm using MS Essentials on Vista home premium. Somehow I have lost the menu
item (Start or Control Panel?) to start it. Security Center reports that
Essentials is running, but I cannot start a scan. All attempts at
reinstalling Essentials have failed.

(I used to use AVG, but after an unwanted upgrade to V9, the PC became
unuseable due to AVG processes taking all the processor resources).

What to do now?