I am going to include the "Hard Reset" steps below, since I don't know what steps you followed and these steps should work. Also, no there wouldn't be a button on the back of the phone to reset it. The only other reset I know of would be in the phone's settings, but that will only work if you can get into the phone.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the phone.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the phone...
1. Make sure that the phone is actually powered off.
2. Remove your SD card, if there is one in the device.
3...