Get a laptop cooler, which is basically a pad with fans that you put under your laptop that can cool it off. Macbooks weren't made for gaming, and mass effect is a pretty demanding game.
ANSWER TO YOUR QUESTION: it can shorten the life of your CPU, but considering how long cpus last anyway, by...
ok, I'm starting to think you might have reset it by a hard turn off. It's kind of common with PC's. just pull out your BIOS battery. If that doesn't work, then it might just be the battery.
Try considering an HP g7 if your on a low budget since it comes with an apu with Radeon HD graphics, or if you have a lot of money to spend, an Asus G75, those things are powerful.