Why won't my nikon cookpix p520 turn on, it's dead

1. Did you hold down the HOLD switch for several seconds? (On top, next to Shutter)

2. Have you inserted a different battery

3. Is the camera really not starting, or is it instead the display is black.

4. Have you tried inserting a different SD memory card. Many of the SD cards now will cause some cameras to freeze, either because they are too high capacity (older cameras) or SDHC (older cameras) or not formatted properly, and other reasons.

Hold down the HOLD Switch
Use a different battery
Use a different SD card.
See if flash works and it is not just a black display.