Here are a few things to check:

• Is your copy of Graphical Analysis up-to-date?
• Check the cable connections. For most Go Direct sensors, an LED will turn on when the sensor is connected to power. The sensor user manual will have more information about what different LEDs indicate.
• Quit all of the following programs:
  • Logger Pro
  • Logger Lite
  • Graphical Analysis
• Re-open Graphical Analysis.

Are you running Logger Pro or Logger Lite at the same time? While Logger Pro and Logger Lite can’t connect to the Go Direct sensors, they can connect to the other hardware that is compatible with Graphical Analysis. To prevent confusion between the apps, we only allow one program to connect to sensors at a time. The other programs will not attempt to connect while something else is running. If Logger Pro or Logger Lite is running and the Go Direct Sensors aren’t displaying in Graphical Analysis, Logger Pro or Logger Lite is probably the program on the computer that is allowed to communicate to the sensors. To fix this you need to quit Logger Pro/Logger Lite and Graphical Analysis, and then restart Graphical Analysis.

This issue can also be caused by a bad battery in the Go Direct sensor. See Why won't my Go Direct sensor turn on?.