Make sure your device has sufficient battery power. Dead USB flashing works when your device is OFF but needs enough battery power when flashing is done and your device is ready to reboot.
Firmware files – these are CFW or OFW files. You can get the Original Firmware files via Navifirm. Download Navifirm .
For Cooked Firmware, just search it on Google. There are a lot of CFWs in the net but use CFW by
CFWs are made of stability and speed without sacrificing the battery life. Use CFWs for Nokia X7, N8 and Pureview 808.
USB cable for your device
Make a back up your files
Take out your microSD card