I'm sad to say that's not a good sign. Your hardware might be damaged.
But if the hardware is still ok, the 15 sec restore would be the path the bring it back from the brink. To do this, hold the pushbutton. After about 15 seconds you'll see the red LED blink (the one near the USB connector), just a very quick flash. Release the pushbutton when you see that quick blink. The restore process takes about 1 minute and you'll see the red LED on continuous & bright. Just let it run until the red light turns off. The board should reboot and if the process works, you'll see the orange LED blinking again, the same as it did when the board was brand new.
If that doesn't work, odds are strong the hardware has a problem. Your first thing to check is the 3.3V power. Just use a DC voltmeter to measure it. Of course it should be approx 3.3 volts. If you get close to zero volts, that's a sign something metal is shorting the 3.3V power to GND. Usually a metal short is fixable if you can find and remove the piece of metal. If you get a low voltage like 0.5 to 0.9 volts, I'm afraid that usually means 1 or more chips are internally damaged and causing the power to short. Typically semiconductors cause a short with that sort of voltage, rather than nearly zero as metal does.
I hope you can also understand how difficult it is to help you when we have so little information. I spent a few minutes just now typing this "cover all the bases" message because I know so little about the problem. I want to help, so I hope you'll consider putting more details into your messages. For solving technical problems, details matter.
