To troubleshoot it further... go the the MDC Firewall Detailed Information link: »192.168.1.254/xslt?PAGE=J14
Look at the section call NAT Sessions.
The first two lines under there are unique and will tell you how many (x) of x/1024 sessions you are currently using. If you get too low, your router will crash.
You can do a find/highlight the particular IP addresses of interest to see which computer/device is generating the massive amounts of sessions (in your case the one associated with windowseven). You can also see if there is a common website or destination IP that also keeps coming up. As your malware checks came up fine, it might be a particular website you visit.