Mid-2009 Macbook Pro won't boot up

[atizzle]

Last Friday, my MBP randomly shut down while in use, even though the battery was charged to about 50%. No sounds whatsoever whenever I hit the power button, no sleep/power indicator lights, nothing except for the battery indicator lights. I've tried a PRAM reset and a SMC reset to no avail. Tomorrow I'll go to my nearest Apple store, but I'm just wondering if anyone here could make some educated guesses as to what the problem could be.