Hi,

After a varying amount of time (from 2 mins to 2 hours) the mouse and keyboard (wireless USB) freeze and I can't control the PC. After several more mins, the PC will swith off.

The PC has been running fine for over 1 year, has been maintained, and is free from viruses and spyware. Batteries are fine.

I tried installing a USB 2 card and plugging all usb into that, but same thing has happened.

Any ideas ?

What do you mean batteries? You say PC but it only have one battery.

Is the interior clean of dust and dirt. Is the system free of malware?

I mean the batteries in he wireless mouse and keyboard.

Free of Malware, not so free of dust. You think it could be overheating? I would excpect some warning. How hot should it be? Currently shows CPU 40, Sys 60

Unfortunately, sudden systems freezes can be caused by many things, which makes it difficult to troubleshoot.

Heat is always suspect. The temps you listed are a bit odd. 40°C is fine, but 60°C for the system is a bit high. What did you measure them with? That said, heat problems usually reveal themselves after the system has had time to warm up a bit. That said, heat is the bane of all electronics so if you have a layer of heat trapping dust inside, removing it is a good idea.

I NEVER trust wireless keyboards or mice. They are great when they work, but often they don't and can cause headaches trying to troubleshoot. So you should always keep a spare, wired mouse and keyboard handy when troubleshooting. If it does it with the wired input devices, you know the problem is inside the computer.

A stressed, slightly out of tolerance, or failing power supply can cause freezes and reboots. I use a FrozenCPU Ultimate PSU Tester for power supply (PSU) testing when I am away from home. It is not as good as a qualified technician testing the PSU under a "true" (realistic) load with an oscilloscope or power analyzer, but close. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you can better detect a "failing" PSU, or one barely within specified tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, not a true load. Alternatively, you can swap out the PSU with a known good one that meets the computer's power requirements.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This then requires poking (with some considerable force) two, hard and sharp, highly conductive, meter probes into the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it.

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.

Be sure to first power down, unplug the computer, and keep yourself discharged by touching the bare metal of the case.

And to make sure it is not malware related, I recommend you purge your system of clutter using Windows (XP or Vista) Disk Cleanup, ATF Cleaner or CCleaner. If you use CCleaner, then during installation, uncheck the option to install the Yahoo toolbar and before first use, go to Options > Settings > Advanced and ensure Only delete files in Windows Temp folders older than 48 hours is unchecked.

Note: Ensure you know your site credentials (user name and password) for sites you frequent before cleaning; you may have to login again at next visit.

Then download, install, update, and run Malwarebytes's Anti-Malware (MBAM) to ensure your system is free of malware. Then do the same for all other computers on your network (everything on your side of the Internet gateway, typically a cable/DSL modem).

Used Malwarebytes etc, so I'm pretty sure it is hardware.
Cleaned out the dust, still same problems for a while. Several restarts later,it wont boot at all
Does bois fine, then freezes on SATA bios
Couldn't see any damage capacitors.
Will be pulling it to bits i guess.

Hmm, well don't forget the PSU and keep us posted.

Motherboard is an MSI K8N diamond plus which has this odd heatsink and heatpipe arrangement for the chipset. I noticed the small heatsink where the heapipe comes from was hot to touch. I put a small fan on it, and th PC seemed to be fixed.

but it lasted 24 hours, then would not boot

When i get the PC back, it is working fine again, haha!

I disconnected all fans except CPU and NB, still running so far, so I can't be sure it is overheating problem.

Not tried a new PSU yet, will do though tomorrow i think. In the hardware monitor "Core Center" it shows the voltages, the do fluctuate a little, is this normal.
+12 is 12.10 to 12.28
+5 is 5.28 to 5.31
3.3V is 3.25 to 3.30
Vcore is 1.37 to 1.39

If it does turn out to be that the chipset is overheating, Could this be due to the reading of +5v shown above, or does it mean that there is some fundamental problem and i need a new motherboard? I know you cant say for sure, but best guesses are good

Will update when i try new PSU

The ATX standard for +5V rail is ±5% so it would seem yours is high and that may have something to do with. Some fluctuation is normal, but it should not be wide swings. My +5V, according to System Information for Windows (SIW), swings from 4.89 to 4.92V.

If it does turn out to be that the chipset is overheating, Could this be due to the reading of +5v shown above, or does it mean that there is some fundamental problem and i need a new motherboard? I know you cant say for sure, but best guesses are good

I'd go for (hope!) the PSU first, before the motherboard.

Fixed it, hooray!

New PSU did the trick!

Bought a PSU tester, it tested as ok though. I did notice that the voltage levels fluctuated a bit whereas on the new one the were rock steady. I guess that was it!

P.S. The PSU tester shows 12V2 as low (beeps and says low) if just the 24 pin connector is in. But if i put in the extra 4/6/8 pin 12V leads it is fine.
I have another PC which does not take an extra 12V connection on its mainboard (allthough the PSU does have one) so if I just test its (20-pin) connector, I get a low warning.
Is this just becasue I bought a cheap PSU tester, or is it my understanding of it?

That's just how some testers work. I am glad the PSU did the trick, and thanks for the followup.