Answer to: Can I fix the hook for the locking mechanism?Had the same problem on the exact same machine. Here's how I solved it. It turns out that at some point, the sleep light indicator cable had been routed in front of the lower case's latch mechanism, rather than on "the inside" of the latch (towards the laptop's guts I mean). Just the extra thinness of that cable pushing against the latch was enough to keep the hooks on the lid from achieving strong enough contact with the latch built into the bottom case. Re-routed cable, and presto. Never had another problem with the laptop staying shut.
Answer to: Keeps Going Into Sleep ModeI am having the same issue with the exact same laptop. In my case, I've discovered that my problem is the left fan, which is not operating or spinning at all. The right fan was filling up with fluff due to having to pick up his brother's slack, and could barely spin itself it was so bogged down. I discovered this by installing iStat Pro right after turning on the computer, and before it went back to sleep I did manage to get it to open- it reported right fan, many RPMs, left fan- 0.