HTC Windows Phone 8S- Hard Reset Steps

1. On the Start screen, slide to the left.
2. Tap Settings > About (informations)
3. Tap Reset your phone, and then tap Yes .
Second method:
1. From the Main Menu choose Settings.
2. Then tap About and select Reset your phone.
3. Confirm the whole operation tappind Yes.
4. Turn off your phone.
5. Press and hold the Volume Down button, and
then briefly press the Power button. Release the
Volume Down button when you see an icon on
the screen.
6. Then press the following hardware buttons in this
sequence: Volume Up > Volume Down > Power >
Volume Down
The device will now start the reset process. Please
allow a couple of minutes for it to complete.

That's all