PS4 controller light flashes blue then the controller turns off

Solution 1:

I had the following symptoms:

• PS4 unused for 6+ months
• When pressing the PS button on the DualShock 4, the LED would blink a number of times with a blue light, then stop blinking.
• The controller would not connect to the PS4 if the PS4 was ON.
• The controller would not connect to the PS4 even with a USB cable connecting the two.

None of the solutions found on the internet would help.

Solution: Charge the controller for 30+ minutes. After that everything was working again. Apparently the controller was out of juice, but had enough juice to blink the LED.

TL;DR: Try charging your controller first.