Succeeded an SMC restart, but my MBP won't start

Few hours ago, I was using my MBP on battery and I realize that my battery icon on the top right corner of the screen is showing an X marks. And when i clicked it, it says 'no batteries available'. I was thinking it's just a faulty operating system, so to make sure my battery were running, I plugged the magsafe power adapter, but it shows nothing but green light as the battery was full. But in fact, my battery was something around 58% when i was using it.

So i unplugged the magsafe adapter, and the computer screen goes black, but the white power indicator on the right side of the mac is turned on, as it was on a sleep mode. So I hit a few buttons to wake it, type my password, going back to the desktop but the battery still not recognized with an X marks. And then I close the lid, but the LED screen wasn't going off! My apple logo still lighting up so bright, and then I open the lid, and force shutdown my Mac hoping that it will fix any problem as usual.

I hit the power button to start my Macbook Pro, but it's just sitting there and no response, no gray screen, no startup sound. And I checked the battery by pressing the battery power indicator on the left side. It doesn't light up at all! I think it should be 4 dots or 5 dots. Or 1 dots blinking if the battery is below 5%. But not a single dot lights up. So i plugged my magsafe power adapter and the LED isn't turning on.

I browse a few discussions on this apple support communities, and found some useful fix. I did an SMC restart by pressing shift, control, option, and power button at the same time for a few seconds, and the LED on the magsafe power adapter turned green, and then orange as if it was charging a battery. So i think that my battery has been recognized and being charged, I hit the power button once again. And still no luck. My mac won't start.

Do you have any ideas what's going on with my MacBook Pro? I've been using it for video editing, visual effects, play some Steam games, and some other stuff.

I wasn't thinking to open the back of my Mac to unplug the battery and plugging it back again. I haven't find the right screwdriver for the screws.

Oh, here's the system specs in case you need it:

13-inch MacBook Pro, Mid-2012, Intel Core i7 2.9GHz, 8GB RAM, 750GB HDD, OS X Mavericks 10.9