I have a cable modem plugged in directly to ethernet (no router)... whether I just "hide" or if I change the MAC address, I lose my Internet connection completely.

Which makes sense since my ISP identifies my account by the MAC address, right?

So what's the correct way to use Hide My MAC and still be able to use my Internet connection?

Thanks!

You should not be losing your connection.
Exit the software completely; then right click on the software's desktop icon; left click "Run As Administrator" and see how that works. If it doesn't write to staff@hide-my-ip.com so we can get an analysis of your computer.