Asus Fonepad display Question (?) mark

Hello, I purchased Asus Fonepad couple of month back. I saw unbelievable thing on last week, charging logo is replaced with question(?) mark. Then I tried to hold the volume down+power button down, hold the power button down for few seconds, charged it for few hours but get no result.
Let me know how to recover this?
Thank you in advance for your kindness.
