System Scan Won't Start

So when I attempt to run a system scan the dialog won't show up. Nothing indicates it is attempting to scan or that it is scanning. Quick scan functions normally with no issues. I have restarted the system and have repaired the software as well. Any suggestions on this? I have had this happen before and it some how cleared itself on its own. Except to day it is preventing me from logging into work VPN due to full scan not functioning.