Computer freezing up every hour or so!

My issue is that anywhere between 1 and 2 hours the computer will just totally freeze up. Complete unresponsiveness of the computer,I got to do a manual reboot . my mouse isn't moving and keyboard not responding to control-alt-delete or anything at all. I can't figure out if the issue is hardware related or software. temps seem to be fine and cool. I have five fans in case and a big fan an heatsink on cpu. I tried a Different harddrive, Psu,and Video card but still freezes up! I reinstalled xp no help! so that leaves the Memory, motherboard or the Cpu. i'm doing memtest on memory now. I wanted to post this and see if anyone has any suggestions. P4 2.4ghz 2 gb memory 500 gb harddrive ati 9600 video card abit ic7-g motherboard

temps seem to be fine

And what are they?

Is the interior of the case clean of heat trapping dust and dirt?

Inspect the motherboard for bulging or leaking electrolytic capacitors. These failed or failing capacitors are a common cause of sudden, but seemingly random system lock ups and reboots. The capacitors look like tall soda cans, many of which surround the CPU socket. All older motherboards, and many of today's less expensive motherboards use electrolytic capacitors containing a liquid electrolyte. Failing (including flawed and/or abused/over-heated) capacitors literally bulge at the seams due to excessive internal pressures. Extreme (and very rare) cases result in a firecracker type explosion that can really stink up a room. Typically, electrolyte just oozes from the pressure relief points stamped in the tops of the capacitor casings (seen as a symbol or letter). The electrolyte can be caustic to motherboards and flesh. Look for white to dark-brown, dried liquid or foam on the tops or bottoms of the capacitors. Bulging capacitors are a sign leakage is about to occur.

A motherboard with bulging or leaky capacitors can be repaired, but often it is more cost effective in the long run to replace the motherboard.

A failing, underrated and stressed power supply can also cause sudden system freezes and reboot.

I keep the case clean and free of dust and dirt. I just finish memtest and after 9 hours memory passed with no errors. But computer still freeze up after hour or two, must be motherboard? Here are my temps and voltage.. Voltage CPU : 1.49 V DIMM : 2.75 V +3.3V Voltage : 3.22 V +5V Voltage : 4.70 V +12V Voltage : 11.80 V Processor Fan : 4218 rpm Chassis Fan : 2343 rpm Power/Aux Fan : 3125 rpm Processor Temperature : 42 °C Mainboard Temperature : 29 °C ACPI Thermal Zone : 42 °C Hard Disk Monitoring : S.M.A.R.T Hard Disk Temperature ST3500630AS : 38 °C

must be motherboard?

It "looks" like the motherboard, but it could still be the PSU. The voltages look fine, but what is the wattage? The graphics card could also be doing this. That's why these type problems are so hard to troubleshoot.

Have you done a complete malware scan?

I have an antec 480 watt Psu. it's not video card i swap it out and system still froze. I had my system overclock from 2.4 ghz to 3.2 ghz for about 4 years now so maybe it's catching up with me because i want back to the defalut speed of 2.4 ghz and it didn't freeze for 6 hour. now will bump it up to 2.8 ghz and see how long it works. it's not malware or virus because of fresh XP install.

it's not malware or virus because of fresh XP install.

That's valid only until the machine is connected to the Internet, or to a network with other computers that have Internet access.

If you over-clock, don't! JMHO. But if you do anyway, you should always mention that up front when seeking help - deviations from standards should not be omitted. Not just because it may be important information responders need, but it often results in delays getting your problem fixed. In this case, simply because overclocking can, and all too frequently does cause freezing and rebooting problems, dropping back to the defaults would have been one the first suggestions offered at the beginning of this thread.

Are you overclocking your graphics card too? Hot graphics GPUs and RAM can cause freezes too - I don't see the GPU temp listed.

I happen to like Antec supplies and have used several 480W models. They are great for normal users. Overclockers are not normal users. I recommend you use the eXtreme PSU Calculator Lite to determine your power supply unit (PSU) requirements. Plug in all the hardware you think you might have in 2 or 3 years (extra drives, bigger or 2nd video card, more RAM, etc.). Be sure to read and heed the notes at the bottom. I recommend you set Capacitor Aging to 30%, and if you participate in distributive computing projects (e.g. BOINC or Folding@Home), I recommend setting TDP to 100%. Research your video card and pay particular attention to the power supply requirements for your card listed on your video card maker's website. Then look for power supply brands listed under the "Good" column of PC Mechanic's PSU Reference List. Ensure the supplied amperage on the +12V rails of your chosen PSU meets the requirements of your video card. Don't try to save a few dollars by getting a cheap supply. Digital electronics, including CPUs, RAM, and today's advanced graphics cards, need clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room. I strongly recommend you pick a supply with an efficiency rating equal to, or greater than 80%. Look for the 80 Plus - EnergyStar Compliant label. And don't forget to budget for a good UPS with AVR (automatic voltage regulation).