if you replace the harddrive you most likely need to also swap out the eagle bootrom (U15) to support the new drive. it needs to be version 2.09 for it to work. if it's version is earlier you will need to change it for a new version.
that said, if you have no video output, I'd look at your video card connection and power supply. even with no hard drive installed the game will still boot and display information on the screen because that is all contained in that aforementioned bootrom and not on the disk.
check your power voltages and make sure you have good 5 volts and 12 volts (also 3.3 volts if you have a red board) if you have a red board it is a standard PC power supply connection, you can purchase a regular old ATX power supply and plug it on there. If it's a green board, you may have to get creative. Suzo happ has replacement supplies, but they are pretty pricey.
also remove and install the video card, it's a pain in the but to do since it's mounted really weirdly, but this connection is a source of many issues.