If your Sony Ericsson ER-LT15I is not good for work, please try the following ways to reset your Sony Ericsson ER-LT15I:
You need to charge your battery, remember to backup your Sony Ericsson ER-LT15I’s important data and in most cases take out SIM and SD card. It is always very important to backup online, because it is impossible to recover your data after doing a hard reset. For all of your data, a backup should be done on an external device, hard drive, raid system or media. Ensure that your important data is backed up in a safe place.
press the Menu key
-scroll to and choose Privacy
-scroll to and choose Factory Data Reset
-choose Reset Phone
-choose Erase Everything
And always remember that this will reset everything back to factory default settings, remember to backup your Sony Ericsson ER-LT15I’s important data at first.