Blue circle with red flashing lightning bolt

My phone drained and now I can't open it.

I've already charged my phone for 8 hours and every time I press the power button, it only shows me a blue circle with a red flashing lightning bolt in the middle.

How long should I keep it charged? Should I bring it to a technician? What should I do?

Please answer fast, I still have loads to do and it's due this week