Hi, I don't really know much about computers.

Anyhow, my cpu is around 2-3 years old, and it is a AMD Athlon 1.4ghz processor. My cpu's usual temp with ASUS Probe is around 60-61 degrees, and it often freezes or the computer reboots by itself. However, if I underclock it to 1.0ghz, it never freezes and temp is around 58-59 degrees.

I would like to have a stable 1.4 ghz computer, not underclocked 1.0ghz computer. Any ideas??

anomy,

The extra speed @ 1400 creates extra heat, and apparently your particular CPU becomes unstable at around 60-61°C

It's probably just a build-up of dust (over several years) in the HeatSink for your CPU.
The dust adversely affects the efficiency of your HS, so your CPU runs hotter now than it used to.
A can of compressed air will blow it out, or, if you promise to be careful, you can use an ordinary vacumm cleaner, and set it on 'blow'

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No, it's not because of the dust formed because I have cleaned it, and I do clean it several times per month.

I've been running a program that came with my motherboard called ASUS Probe which tracks CPU temperature. I've discovered that when I assign my computer, for example, many programs to open at once, the temperature all of sudden goes up to 110 degrees from 60, and after couple of seconds it goes back. I dont think a better cooling fan would solve this, any idea why this would happen? I've set the Vcore default and lowest 1.75 under BIOS.

anomy,

Well, it may not be the 'dust bunnies', but it is still an overheat problem.

Prove it to yourself... try pulling the side off of your case, and set up a small desk fan blowing cool air directly into the box. See if that helps.
If it does, then you KNOW it's a heat problem, and now it's just a question of 'Which component?'
In all likely-hood, it's your CPU, and possibly just a re-application of Thermal Paste will solve it.
But if your temps are shooting up from 60° to 110°C? then you have a serious problem that you need to fix NOW, before you fry that Athlon 1400

Those old Athlon 1400 CPUs all ran really hot... they consume as much (or more) power as the much newer, and faster, Barton 2800+
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and: http://www.cpuscorecard.com/cpuprices/aaxp.htm' ">http://www.cpuscorecard.com/cpuprices/aaxp.htm

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Thank you, Milt for your help. I'll see to it that I get a better cooling system for my Athlon CPU. Yesterday, I underclocked it from 1.4 to 1.2, and so far it seems to be stable. Not that bad having 200mhz less of a speed...