Try the troubleshooting steps found at:
Colorimeter Troubleshooting and FAQs

Common symptoms of a malfunctioning Colorimeter include:
     – Pressing the arrow buttons does not switch between wavelengths
     – Wavelength indicator lights are not lighting up
     – Absorbance values are not being displayed in Logger Pro, LabQuest App, or Graphical Analysis 4
     – The LED light sources are not lighting up and cannot be seen when the top to the cuvette holder is open

If the problem is still not fixed, see What should I do if I have a piece of hardware that needs to be repaired? for instructions on obtaining a Return Merchandise Authorization number.

If there is a manufacturing defect in the Colorimeter, we will repair or replace it at no charge if it is within the five-year warranty period.

However, Colorimeters often malfunction because they have had liquid spilled inside causing corrosion. If this is the case, we will let you know if it can be repaired or if it is beyond repair.

Liquid has spilled inside my Colorimeter. What should I do?