I don't have enough info, so I'll go over basics:
// If you are using a Tower
Unplug the computer, hold the power button down for 30 seconds, replug in. Should start up
// If using a laptop
Pull the AC, remove the battery, hold power for 30 seconds, plug in the ac (not the battery) Should turn on.
//If you are using Windows 10
You probably had a windows update that ruined the PS4 drivers.
Jump to google and see what you need to download to repair the driver. Windows 10 is notorious for doing this.
Worst case scenario: use the System Refresh (not restore). You'll have to reinstall programs, but your files will be fine.
//If you are NOT using Windows 10
Your third party program that is used to map a 360 controller into a PS4 controller is busted. Uninstall everything and reinstall it.