Many issues that you encounter when using Logger Pro can be solved through the following process.
1. What version of the software are using? In many cases, a free update will resolve the problem. To find out, open the software and choose “About XYZ”. The exact version number will show in this window. Updaters for all of our programs are available at:
http://www.vernier.com/downloads/soft.html

2. Make sure the interface has power. For troubleshooting purposes, use AC power instead of batteries. If you are using LabPro, the unit should make the “happy sound” after it powers up. If you are using LabQuest, both the screen and power light should be lit.

3. Check all of your cable connections. Make sure that one end of the cable is completely plugged in to the interface and the other end is all the way into the computer.

4. If you have multiple computers and interfaces, try methodically switching interfaces, cables, power supplies, and computers to see if the problem is with a piece of hardware. The best way to do is to take one of your completely working stations, and try swapping in a different interface, then a new connector cable, etc. If you can trace the problem to one of these pieces, we can probably repair or replace that part.

More troubleshooting tips for using Logger Pro are available:
Logger Pro Troubleshooting and FAQs

If you are using an interface or other device that may be having problems, please see below for more information:
Original LabQuest Troubleshooting and FAQs (Full List)
LabQuest 2 FAQs
LabPro Troubleshooting and FAQs
The LED on my Go! device or LabQuest Mini is not green. What does that mean?
Ocean Optics Spectrometers Troubleshooting and FAQs
OHAUS balance Troubleshooting and FAQs

Extensive help and troubleshooting tips for each sensor is available on the individual sensor’s page:
http://www.vernier.com/probes/index.html