My Macbook shuts down all of a sudden!

I usually let my Macbook sleep while a DVD's inside and I never had any problems with that. But it has already happened twice that when I open my laptop, the DVD starts whirring (which is normal) but after several seconds, the DVD pops out all by itself. Then my Macbook goes black, as if it's shut down but the sleep light constantly stays on, as in, not slowly blinking like it's just sleeping.

Pressing the power button for several seconds restarts it as if nothing happened.

Just wanted to know what's wrong with my laptop before these random shutdowns start to interfere with my productivity. Thanks.

For one, it's not a good idea to leave a DVD or CD in the drive and then put the machine to sleep. You may wind up with not being able to remove the media...

Try resetting the SMC on your machine by following the directions given in this Apple KB article. LINK