You may be experiencing any of these issues: 

• Unable to charge the phone while it's on
• Receiving System Message: "Phone is in USB host mode - Unable to charge while in host mode" while not using an accessory that is designed to enter USB host mode, such as an USB On-The-Go cable

This message usually appears due to a damaged charging cable, resistance in the connection, or a damaged charging port on the phone. Use this checklist to help identify the issue:

• Ensure that the USB charging cable and wall charger are the HTC branded accessories provided with the device, and that they are in good condition. 

• Ensure no extension cords, surge protectors, or USB hubs are used. 

• Ensure that the charging port on the device is clean and free of debris, if foreign material is located please make use of a soft brush to clean the charging port. 

• Ensure that the HTC branded cable is working when used with other phones either connected to a wall charger or PC. 

• If the device has Fast Boot (HTC Sense 6.0 and lower), disable this setting and try again.
   

If the issue isn't resolved follow these steps: 

1. Perform a soft reset using the hardware buttons.

2. Clearing the data cache may resolve the issue. See How to Wipe Your Cache Partition.

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