LG ENV3 shutting down automatically

The problem you have mentioned can be rooted out by any of the steps mentioned as below:

By upgrading the software of the cell phone-

The latest software for LG enV3 is VX92KV03; you can download it using LG Software Updater without any surprise. The update will take you about 10 minutes without any surprise, in the meantime, do not plug out the USB cable. 

You have to install LG Mobile Software Updater Application before download manual, software or latest firmware for your LG env3. Please check up whether you’re PC can support the following requirement.

1.     1GHz or higher Pentium-compatible processor

2.     At least 256 MB of RAM (memory)

3.     Windows 2000 (SP4 or later) or Windows XP (SP1 or SP2), Windows Vista

4.     Administration rights on the PC for software installation

5.     High-speed Internet connection

Preparation Requirements

1.     Fully charge the battery.

2.     It is recommended that you save any important data onto the PC using the PC Sync. Feature.

3.     Close PC Sync/applications before proceeding with the update.

4.     Calling and messaging functions are not available during the update process.

5.     Remove the SD card.

6.     Do not disconnect the USB cable until the update is complete. Disconnecting the USB cable or interrupting the update process before it is complete may cause your handset to fail to operate.

7.     The handset is automatically reset during this process.

8.     The update takes approx. 10-30 minutes depending on the model and downloading environments.

I am sure that after this process you will be able to overcome the problem of your phone.