Hi Siddarth,
The eye tracker will only light up if there is at least one Tobii EyeX client application running. It is unneseccary for the eye tracker to be tracking if no client application is interested in the data.
You can check if this is what is happening on your system by closing the Settings panel so that the eye tracker is no longer lit up, and then hovering over the Tobii EyeX icon in the notification area: when there is no client application using the Tobii EyeX Engine there will be a mouse over message saying that “There is no application that is using the eye tracker”.
Since the Tobii EyeX Settings panel is a client application, opening it leads to the eye tracker lighting up.
But still, what changed on your system the day before so that the behavior of the eye tracker changed? It seems some EyeX client application is no longer running. It could be that the EyeX Interaction software, which is included in the EyeX Engine install, is no longer running. This software is what makes it possible to use EyeX Direct click for example in the Windows Start menu, and EyeX scrolling in Chrome.
You may have accidentally switched off EyeX Interaction. There is a switch in the EyeX Settings panel on the left hand side next to the text “EyeX Interaction”. It is orange when enabled.
Or, maybe, the EyeX Interaction software stopped working for some reason. You may have to reboot your system to get it working again (or just restart the Tobii Service in the Task Manager).