Before you buy a new cell phone or new tablet, please try the following procedure to repair your device. First charge your battery, backup your important data if possible and in most cases take out SIM and SD card. It is impossible to recover your data after doing a hard reset, so online backup is always important. For all of your data, a backup should be done on an external device, hard drive, raid system or media.
LG T515 Cookie Duo hard reset
To reset your LG T515 Cookie Duo phone to factory settings and erase all the data on your phone, touch Menu > Settings> Privacy > Factory data reset > Reset phone.
You can use LG Mobile Support tool to repair your LG cell phone, after download select menu Customer Support > Recovery Phone
If you know hard reset using buttons pls share in comment.