A SX EZTRAK should not have a hard drive. At the age of your machine, it may have been retrofitted with one. If so, the hard drive may be the issue.
The first 2 EZTRAK machines that I installed with hard drives from Bridgeport would do the same thing. Totally lock up. The problem was a vibration issue interfering with the hard drive reading. Thus the invention of the hard drive suspended on springs.
Check logic power supply voltages and its fan.