Not to worry, it is possible that your mixer may just need a good cleaning. If you spilled an excess of liquid onto it, it is possible that the slider has been stuck in place by the liquid. Cleaning the slider from the inside of the handle may fix this problem and allow the slider to move with ease again. If your problem persists it is possible that a piece of the slider could be missing or a part of it is caught on something inside the mixer’s handle. To fix this issue you will need to replace the mixer's speed lever, by following this speed lever replacement guide.
If you can hear the power button clicking but the device will not turn on, it could be because of a faulty power cord or a bad connection somewhere in the device. To fix this issue, you will need to purchase a new power cord and install in on the device. Please follow this link on how to replace the power cord in your device.