try soft reset, please try the following:
Hold the two buttons (power+volumeDown) until it vibrates, release it and it will vibrate 3 times and restart.
If there is enough battery the phone should restart normally.
If not, please follow the instructions below:
- Download the NSU (version 4.0.1 for retail). Install the suite to your PC (Windows 7 & 8 only).
- Simply plug in your Windows Phone to the PC, fire up the software suite and choose "My device doesn't boot up."
- Once the device connection screen shows up, press and hold the power + volume down buttons simultaneously until the phone vibrates.
- The software will then detect your Lumia Windows Phone and prompt you to install 1.2GB worth of recovery.