I'll start this off by saying I'm not the most tech-savvy.
Recently my computer has been getting the random shutdowns that overheating causes, and upon startup after this happens I get the MIT overheated message.
Now, from what I've gathered my current power supply is 'bare minimum,' and I assumed that also applies to if I try to get any new type of heatsink or fan I would need to upgrade my power supply as well.
I've had my computer since Christmas '09, and I'm kinda disappointed this is happening already. (problems, I mean)
Now I have an Asus Essentio 5290. I've heard it's not the most well-made PC, and I have had problems with it such as sound-tearing and some hardware problems before as well, but they're bearable and fixable.
You are right, you shouldn't be experienceing overheating. I couldn't tell you much woithout knowing specifics about the case and vetilation.
I suspect you have some clogged fans. This happens especially if a PC is located near the floor and pet hair is a particularly nasty problem.
If you haven't alredy, get a can of compressed air and open your case panel. pay particular attention to intake, exhaust, and CPU fans. Clear as much dust as you can and once the inside is clean, start up your pc to ensure all fans are sipinning.
Be careful! those fans are sharp. I would carefully check to see if there are any hot spots within your case. Sometimes the cheapo oem cases are missing an exhaust fan or an intake even. See if there are any open spots for adding a fan or two.