Desktop will not load with defense and security level set to active.

When i set the defense and security level to active and do the restart the desktop will not load. I have to start the computer in the safe mode and deactivate the defense and security level and do a restart and then everything is ok. I’m using avast anti virus and am wondering if this might be part of it. I tried turning off the start up of avast and still had the problem. I’m running vista software.
Also Comodo Bo clean. I’m not using any other firewall or antivirus.

Any suggestions???