I called Hamilton support today (1-800-837-5561) and they dialed into my modem and checked out my credit card computer. They said that the unit was turned off for a very long time and it was reset a lot of times. So apparently they can not really check anything by dialing into the system. (I knew that much!) They did say to send the unit in to them and they think it will cost anywhere between $200 and $500 to fix.
Hamilton entry unit problem
William was trying to show me how the entry unit works and the Hamilton handheld would not work. (The handheld, from what I have gathered, programs prices and the credit card computer.) William called Hamilton to try and get the handheld to work but nothing would work. Ends up that the cord was messed up (last picture).
I took the $1900 Hamilton credit card computer home with me to fix the handheld cord, which I did. I did not take the 2 boards apart but the top board looks like an Aprotek modem.