Sometimes the Tobii eye tracker turns on and off rapidly when you connect it.
A "blinking or flashing" Tobii eye tracker is usually the result of a lack of sufficient power to the USB port it is plugged into. If you have multiple USB ports where you can connect your Tobii eye tracker, try moving it to a different port. Having the eye tracker plugged into the opposite side of the computer from the external monitor often solves the issue. If this is not possible or it doesn't work, try adding a powered USB hub. A powered USB hub plugs into a main electric socket and connects your devices to your laptop/PC. You can purchase a powered hub from any computer accessory supplier or through the Lexplore shop*.
*The Lexplore shop is for UK schools only.
Here is a video showing you how it works.