Macbook pro 2010 blanks and freezes

I cannot leave my Macbook pro 2010 13" OS X 10.6.8 alone for too long, or else the screen goes black, it goes into hibernate, the fans run, and I have to spend 20mins-3hrs waking it up. Pressing restart doesn't always help. I don't let it Sleep. Always have to turn it off and on whenever I need it.

I have to make sure I always have it well-charged and plugged in when I start it, b/c sometimes that plays tricks. Occasionally, not. I don't know if it's a factor. I play it safe now.

The internet runs slow. I switch btwn Safari and Chrome. Accessing files takes a time. I have mainly .doc tho.

I've never spilled anything or done anything to my computer, or dropped it. The fan runs hot, though I never game. The hardest thing this computer does is Netflix binges and Google Plus Hangouts, occasionally Photoshop.