If you attempted a hard reset (How do I perform a hard reset on my original LabQuest unit?) and the blue light did not turn off and the unit did not reboot, it is possible that the reset button on the back of the LabQuest stuck or broken.

In this mode, the LabQuest will appear to be OFF and the blue light will not be on. It will appear as if the unit does not charge. Once the button is released, the blue light should go on and the unit will reboot.

Most of the time, it is because the button is off to one side and not popping back out when released. By pushing the button slightly to the side with the stylus, it will release.

To test if the switch is working, put the stylus on the reset button, then look at the face of the LabQuest. When you press the reset button, hold it down for two seconds. If the blue power light does not go off at all, the reset switch is not working, and the unit will need to be serviced.

If the blue power light goes off, the LabQuest should reboot, which will take about three minutes.

If the LabQuest still does not reboot, please contact Vernier Technical Support to arrange a repair. For a temporary fix, you can remove the battery. For instructions, see:
How do I remove or replace an original LabQuest battery?

See also:
Original LabQuest Battery Troubleshooting and FAQs