Possible that a core dies?

Is there any possibility that a core could die within a laptop? I have the 2008 MacBook Pro with the Core 2 Duo, and i have noticed that as of late, when i do video production and handbrake encodings, it takes 2x as long as what it used to months ago. Like a handbrake encode went from taking an hour to two and half, or a premiere pro encode takes 6 hours for a 1080p 30minute video. Now i did downgrade from Lion to Snow LEopard since i was having GPU issues, which i think has extended into SL now since Starcraft 3 doesn't play at High like it used to, now it can't go past Medium. So, any idea what could have caused this slowdown?

 

Ok, i'll check that once i get home from work today. I didn't think about checking Activity monitor.

Yes TSBrick my MAc will get considerably hot, but i do have it on a stand which keeps it elevated, but i generally can't touch it since it's so hot. But it has always been like that, after getting 3 GPU replacements over the years, you would think that would have been fixed.