Hello! Recently (just last 24 hours) I started to have this unusual problem with Security Essentials. Firstly, i paid attention that before booting to welcome screen Windows wants to run checkdisk but fails due to an unspecified error. Secondly my Security Essentials is turned off - I can't turn it on, nor i can't uninstall it nor upgrade it through new install file. I didn't install any new program in days - last one was Deus Ex from Steam a month ago.