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Possible Duplicate:
Task Manager shows 100% CPU utilization, but nothing in process list does.

My friend has a machine in his teashop that I am attempting to troubleshoot, so far with minimal success. It is a WinXP, 500MB, 2.12GHz. Nothing spectacular by today's standards, but a reasonable piece of equipment.

In the last couple of months, it has started a behavior that I have so far been unable to repair. When the machine sits idle for a while, it suddenly jumps to 100% CPU usage for no apparent reason. It has WinAmp running almost constantly, playing background music in the teashop, and usually a browser open, which the owner plods around on the net when not busy with the shop. This all works well and when WinAmp is running, usage is around 3-5%, as one might expect.

But when the owner leaves the computer idle for some time, the usage suddenly jumps to 100%, to the point where WinAmp can't even keep up - the played sound stutters so badly it's unrecognizable as music. This continues for around ten seconds, then stops, then resumes fifteen to twenty seconds later, stops again, and so on. It only quits when someone moves the mouse or presses a key. This happens regardless of whether a browser is open or not, and I've tried all three of the biggies.

The process names window shows nothing using that much power, although the CPU utilization line is at 100%. And it's almost impossible to do any research into the problem, because as soon as I move the mouse, it stops. I have an anti-virus (NOD32), have checked for spyware, unloaded everything suspicious from the start-up configs and installed a load balancing tool called ProcTamer. Nothing has helped.

Can anyone suggest something to try?

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  • As mentioned, try running Process Explorer as administrator, if it is the System process then it are most likely driver problems. Try the second part of an earlier answer (about Windows Performance Analysis Toolkit) in that case to get an idea which driver is causing the problem...
    – Tamara Wijsman
    Mar 31, 2011 at 14:08
  • associated your accounts, @pdanes.
    – studiohack
    Apr 23, 2011 at 0:42

4 Answers 4

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One way to diagnose this might be to open the task manager pre-emptively.

Switch to the "Processes" tab and enable the "Show processes from all users" option. Then sort the grid by CPU - a single click on the heading of the CPU column should do this (click again if System Idle Process isn't at the top).

Then when the problem starts you should be able to look at this view and see what's now at the top of the grid. Make a note of the process name then search using Google or ask another question for more information.

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  • Chris -> Okay, thanks, I'll give that a try. I'd try it right now, but the shop is where I go some evenings. Next visit, I'll see what this shows and post back
    – pdanes
    Mar 31, 2011 at 13:48
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I would suggest delving deeper into the process list using Microsoft's ProcessExplorer. It will show you all the resources all the processes are using, and even make you some nice graphs to look at. It should pinpoint the process that's doing the dirty on you.

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Does the system have a screen saver when it has been idle? Some of the 3D screen savers will use 100% CPU and impact other processes.

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  • No, there are no screen savers running.
    – pdanes
    Mar 31, 2011 at 13:48
  • AFAIK, screensavers are started at "Idle" priority class, so they cannot impact other processes. (They can use up 100% CPU, but only if no other program needs it.)
    – u1686_grawity
    Apr 1, 2011 at 14:23
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"Interrupts" taking up all your processing power means that a piece of hardware in your system keeps calling the CPU. The first two things to check are your disk drives (is one failing?) and your video card. Update the firmware and drivers, and replace with known good units if you can to test.

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  • Thanks, Hyppy. I have two drives, I can completely disable the second, but not the C:\ drive, or the system won't start. The video hardware is on the main board. I suppose I could try to install a separate card, but if there's something wrong with the onboard stuff, it might cause problems any, no? Is there no way to see which piece of hardware is doing the calling?
    – pdanes
    Apr 20, 2011 at 13:33
  • There's no way that I know of within Windows to determine the source of a hardware interrupt. It goes directly from the device to the CPU by design. You may want to try marking down the model numbers of each of your internal devices and see if there are any known issues for them with regards to excessive interrupts. Sometimes it's as simple as a HD being set to PIO mode instead of DMA.
    – Hyppy
    Apr 20, 2011 at 14:10
  • I'll disable the second drive and see what that does. It contains almost all the music files that this computer plays, so that actually might explain why this behavior shows up when WinAmp is running. I have a swap file on it as well. I've seen remarks about PIO vs DMA. Where is that done? I found some stuff in the BIOS about it, but the remarks I've run across indicated it should be done in the device properties. However, I find no such properties in the device manager's dialogs on this machine. Can you shed some light on that as well?
    – pdanes
    Apr 20, 2011 at 14:51
  • You set DMA/PIO mode under the properties of your hard drive controllers in Device Manager, not the hard drives themselves.
    – Hyppy
    Apr 20, 2011 at 15:03
  • Hm, okay, I'll look at that next visit. I'm looking in the dialog now on this machine and not only is there no mention of DMA/PIO in any of the IDE/ATA controller properties, but all of them are read-only. But this machine is different, with SATA drive, maybe the troublemaker has it as you say.
    – pdanes
    Apr 20, 2011 at 15:36

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