Glo GLO won't turn on, restart or factory reset

[Mengxx]

Greetings!

There is a problem with my kobo glo now. Yesterday when i was reading an ebook in format epub (with the backlight on), it was suddenly frozen on that page so I tried to turn it off. As the turn–off didn't work, I tried to restart it with paperclip, but only the backlight off the screen remained frozen.
When I turned on the power button or charged it with computer/wall charger, the LED between the light button and power button became blue and lasted for about 15 seconds, but it didn't turn to green as normal. I've tried several methods to factory reset including hold light button and turn on power button, press and hold both restart and light button. But the LED didn't become a flashing blue light, still a 15s–lasting blue light. When I connected it with computer I couldn't see the contents in it, but when I plugged the inner tf card in computer with a card reader I could see the content normally. I also took the back cover off and unplugged the battery and replugged it. I have no idea what's wrong with it. It's it excellent condition and hasn't been dropped at all.

Any suggestions would be much appreciated. And sorry for my poor English (。•́︿•̀。)

Thanks!