Why does my zeiss humphrey visual field machine keep shutting down?

This is a brand name, not a specific device and model. That said, here is a page describing mode switch in the setup screen using the touch screen for a specific device. I assume a touch screen would have an icon for turning a device off.
Zeiss HUMPHREY 720i User Manual System Setup

The two most common problems when trying to find a blind spot are: A.) Forgetting to patch the eye, and B.) Choosing the correct eye in the machine itself.

In the user manual they list some compatible printers that have a 25 pin parallel connector. We use Lexmark Optra E312L with good results. Once you hook it up, you have to go into one of the setup menus to port it over. The user guide tells the procedure.

You sjould press the patient button and the same time turn it the instrument on keep in button press until you see in tje display the calibration message of the touchscreen

Did you move the brighness control. It is on the right side of the equipment. If not, it could be the video board inside of the equipment

The trouble is with the CPU. It needs to be replaced

is the cooling fan turning?

I believe "state 19" is a weak main illumination bulb. Not sure if it's the same on your 740, but that's what the problem was with our 750i. Even though the bulb appears to be working, they dim over time and won't pass the start up calibration checks. On ours, there is a round access panel on top of the unit to service this bulb. Just be careful removing the bulb and don't bump any of the clear optical wheels. Part # 2660021106082 (for 750i. not sure about 740) Call Zeiss to confirm. Realize this is an old post so info is for future readers.

erro 99