Once I connect the drive, I get no video signal and a blinking red hard drive light.
The Seagate Barracuda is a computer rated hard drive and is not recommended for your Zmodo system. Computer hard drives require much more power than the DVR can provide. You will need a DVR or Video rated hard drive such as a Western Digital Puple or AV-GP, or a Seagate Pipeline or Video 3.5. You can use any capacity from 500GB up to 2TB.