Quote from MRWSM:
This website says you are better off shutting down when not using to extend the life of the hard drive. My HP was fine all day until after being on for 12 hours and then the hard drive blew. I noticed some dust inside that might have caused over heating although I had no sign of it at all because it's hard to tell on a desktop. Staying on steady would probably make any little problem like dust worse.
When I bought the Seagate HD it is rated at 50,000 cycles on/off or 136 years if you shut it once a day.
http://www.preservation.gc.ca/info/faq_2_e.asp#2
It was the dust.
Dust destroyed my graphics card about 6 or so years ago. There was so much dust, it didn't allowe the fans inside my CPU to spin, I had no idea that dust could collect like that in my computer.
Never had the issue again, but if you never dusted in your computer, or spray some compressed air, that could reduce the life and cause things to become hotter.
I've had my computer running non-stop for the past year and a half now, I only shut it off for 3 weeks over christmas when I went on a cruise, other than that, i reboot it every morning before trading, but it is always on.
No issues.