Something to note, if the camera is offline, and "Manual" is ticked in the property sheet of cell A0, you should be able to press F5 to acquire an image. While online, you can't generally modify the cells in Explorer. Mentioning that you could change the cells and see the values updating on the HMI leads me to believe that the camera isn't "Online".
I don't have a camera handy to test this on, but I think you can set the Trigger value to a cell in the property settings of cell A0. If you double click on the "Trigger" text, or highlight the text and click on the leftmost icon under the menu screen, the cells with a dollar sign, you should be able to select a cell to monitor for the trigger. I don't remember what the cell needs to be to trigger this way though, it's been quite some time since I've worked with In-Sight Explorer.