Why is my laptop not powering on?

I used my laptop without connecting it to the AC. After it prompted me that my battery will soon run out, I connected my laptop to the AC using the charger I purchased with the laptop. It was not charging anymore. After awhile, the battery was drained and I was not able to open the it anymore. I tried resetting the battery using the pinhole found at the bottom of the laptop but to no avail.