Procedures to hard reset HTC One A9.
Hold down the Power key for a few seconds to switch the gadget off.
Press and hold the Volume Down + Power Key at the same time for few seconds.
When you see the three Android pictures, release the held keys.
Press Volume Down to choose “Recovery” option. Press Power Key to affirm. Choose “wipe information/factory reset” from the recovery mode using volume button and Power button to affirm.
Pick “Yes ” to affirm the entire operation. All the data will be reset
After that select choice “reboot system now”.
Now the work is done.
Hold down the Power key for several seconds to switch the gadget off.
Press and hold the Volume Down + Power button at the same time for a few seconds.
Release the held keys when you see the three Android pictures.
Press Volume Down to choose “factory reset”, and press Power button to affirm.
Task is now complete
If the screen is off, turn it on.
From Main Menu go to Settings and tap Backup and reset.
Select Reset phone and select Erase all information.
Tap OK to start the entire operation.