Free Antivirus doesn't Start after Windows 8.1 Update

Hello, everyone. I had the free antivirus working properly, then after I updated from Windows 8 to 8.1, the antivirus didn’t start with Windows. I tried downloading the latest installer and running it, but, as soon as I restart the computer, the antivirus donesn’t run. How can I fix this? Thanks in advance!

Do you mean the icon in the systray is not there but when you open Task Manager you see cmdagent.exe and cavwp.exe running?