HTC Desire 826 has a persistent problem that cannot be solved, you can perform a factory reset (also called a hard reset or master reset).
A factory reset reverts the phone back to its initial state — the state before you turned on the phone for the first time.
Important: Factory reset will remove all data on your phone storage, including apps you've downloaded and installed, your accounts, your files, as well as system and app data and settings. Be sure to back up any data and files you want to keep before you do a factory reset.
Note: A factory reset may not permanently erase all data from your phone, including personal information.