My Huawei tablet doesn't turn on and is not charging. What should I do

I didn't charge or use my tablet for about 3 months. Yesterday when I tried to switch it on by power button, there was no response. Then I tried to charge it by its original charger but only the small red light was flashing and no battery icon was there on the screen. I hold the "power + volume down " keys together for more than 15 seconds but nothing happened. It is not charging at all. It doesn't turn on also. I am in a fix. Please help.