You may be experiencing any of these issues:

• Motion Gestures do not function at all
• Motion Gestures function erratically

The issue may be caused by incorrect Motion Gesture settings. Follow these steps to check that the settings are correct:

1. Go to Settings > Display & Gestures > Motion Launch Gestures.
2. Ensure all settings are properly enabled.

Ensure the phone is fully updated, by following these steps:

1. Go to Settings and select System Updates. The exact path will differ depending on your phone.
   These are the three typical paths:
   
   Settings > System updates > HTC software update
   Settings > Software update
   Settings > AT&T Software Update
   
   
2. Select HTC Software Update to check for new updates.
   If an update is available, follow the on-screen prompts to download and install the update.
   If no update is found, confirm the device is on the latest software version; Settings > About > Software Information.

Your phone's touchscreen may have performance issues. See How to use the Diagnostic Tool to check touchscreen performance.

A factory data reset can also resolve some software issues. See How to factory reset a device.