If the buttons on your 75iv2 are not working:

The 75iv2 has a child safety lock. Do you have the LOCK button enabled? When it is locked, a light will appear above the lock button.
To unlock the control panel: Press and hold the LOCK button for 3 seconds. (You will hear a beep and the light above the LOCK button will turn off.)

If the buttons are still not working, perform the following steps:

1. Unplug the purifier from the wall outlet.
2. Remove the power cord from the back of the purifier.
3. Remove the front panel from the purifier.
4. Remove the filter from the purifier by turning the filter lock counter-clockwise to release, and then pull out the filter using the finger nooks.
5. Let the purifier rest for 30 seconds without the filter or panel installed.
6. Reinstall the filter, making sure that it is placed securely back in the unit (insert bottom of the filter first, and then press the top in and turn the filter lock clockwise to secure the filter in place.)
7. Place the panel back on the unit, making sure it closes securely. 
8. Reinstall the power cord into the back of the purifier, ensuring it is firmly locked in place. 
9. Plug the purifier back into the wall.
10. Press the power button to power on the purifier.

If that doesn't resole the issue, please reach out to Customer Support.