Windows 7 - 64 Computer shuts off unexpectedly

I have a home built Windows 7 x64 computer with a Core 2 Quad CPU. It has recently taken to suddenly shutting down/turning off at unusual intervals. I should note that it powers down suddenly, and does not do a blue screen or shut down. It seems to be most common when playing media. I have tried running SpeedFan, and the CPU temp seems to hover around 49C. The computer has been running fine for over 1 year. Could heat be my problem, and how should I address it?

Steps Taken: (Problem Resolved)

1. Completely cleaned the inside.
2. Reseated the heatsink.
3. Ran memtest 86, which found one memory error, which was followed sometime later by the computer switching off (which leads me to believe it's not the memory).
4. Installed a brand new power supply.
5. Inspected all fans to ensure they are running.
6. Switched out memory sticks. This is not the problem, unless they're all bad.
7. Reseated hard drive cable.
8. Tried with a different video card.
9. Tried the CPU in a friend's motherboard. Same exact problem occurred there.
10. Applied for a warranty replacement.
11. Replaced the CPU, seems to be working now.

Just as a side note, the computer is still running fine, it was definitely the CPU.

Solution 1:

Replace the power supply and stress test your computer.

Reseat (or replace) your heatsink and reapply thermal paste.

Run +memtest on the RAM.

Check all cabling; reseat the SATA/IDE cables to your hard drives.

Clean out the dust as best you can.

--

49 isn't that high of a temp. What heatsink are you using?

Solution 2:

You don't need to start swapping hardware until you have eliminated software as the cause. Check temps first. If they are good I would start with simple tests, like booting to a Ubuntu CD to see if your computer shuts down with a clean OS running. If that works then test your RAM with +memtest. If you have a memory failure pull your RAM out and run +memtest again, testing each stick individually. If you still have not found a problem by now you can start swapping stuff, like your GPUs, PSU, and other stuff.

Solution 3:

If you are using nvidea 64-bit drivers, make sure they are the latest version. I also had several machines rebooting/hanging/crashing at random.