Silly question, but does your router have a built-in firewall? Also, SQL runs on port 3306, I believe, you could try and set a rule to forward that port to your server machine, if all else fails, get wireshark and run a scan on your network interface and see what the packets look like for port 3306. You can also run a netstat -a -o and see that port 3306 is indeed openning. The -o will show you the process ID of the processes that's utilizing that port, it should match with the PID of the processes in the Windows Task Manager. You can see PID by turning on the PID column (by clicking view > select columns) under the processes tab.