I’m at somewhat of a loss to understand why you’re using a second NIC for “extra security” – unless perhaps the external NIC is for your remote access.
If I read your description corrrectly, it looks like your DHCP server is handing out external addresses – but you didn’t confirm that – or tie it to a specific interface.
What I’d recommend is that you hand-configure a couple of IP addresses on the inside and outside and leave the DHCP configuration out of the picture until you have basic IP connectivity working.
Since you provided your DNS IP address (if accurate), you appear to be a commercial Comcast subscriber in the San Francisco/San Jose, California area. I hope the 192.168 addresses you provided were supplied to just keep your address private. If not, there may be other issues.
Open a command prompt and type “arp -a [Enter]” to see if your server has contact with anything else.
Also double-check that you haven’t switched the inside and outside NIC connections.
Write back with a better picture, and we’ll try again.