I've been getting weird high CPU usage/spikes, and I barely have anything open, just a window of my hdd, and this task manager.
I have AMD Phenom II X4 965 @ 4.0Ghz using Corsair H60 cooler w/ push pull
4gb DDR3 Wintec 1600 RAM
I had a similar problem, and had one tough time tracking down the cause - finally managed to diagnose the problem and fix it last night. Maybe my recently gained experience will help.
First, look at the "processes" tab on your task manager, and see if there are any processes running that are taking up the processor time. I assume you've done this already, but I thought I'd just mention it - if you can identify a process that is taking the processor time, then it's just a matter of googling that process to identify what it is, and maybe removing the offending program.
If no process appears to be taking up that much processor time, btu the processor still is being mysteriously used, then what is probably happening is that you've got excessive hardware interrupts happening, and that can be down to many different causes.
To check if this is the case, and it's hardware interrupts that are causing your problem, google "process explorer", and download the program by that name; it's free, and pretty light weight. Install and run it, and you'll see a screen with the processes, and a line called "Interrupts", with the description "Hardware Interrupts and DPCs" - are they taking up the mysteriously used CPU time?
If the answer is yes, then there are a few options. I'm not sure whether it's just an XP bug, or whether it is in other windows versions too, but at least in XP, the the controllers for your hard drives can, in some circumstances, switch to "PIO mode", when they should be DMA, and that can cause excessive hardware interrupts.
Go to your device manager (control panel - system - device manager, on my machine, and I'm translating here, because my Windows is a regional version in Finnish), and check your SATA controllers by right clicking on them, selecting "properties", and searching for the "transfer mode" in the tabs there - it should say something "DMA", and not "PIO" - if it says "PIO", change it to DMA.
If this isn't the problem, then you may have a defective device driver, and the problem now becomes figuring out which device driver is responsible for the interrupts.
To diagnose that, you need to download a Microsoft tool called "RATT". It's a developer tool, and not that user friendly, I found, but ultimately pretty easy to use anyway.
Just get the program, install it, and it'll run. It'll add an icon onto your tray where the bacground processes and running programs are, and you can right click on it to bring up a menu. It'll essentially "listen in" on what is happening on your computer for 3 minutes at a time, after which it creates a log file - a text file - into your windows\system32\LogFiles\RATTV3\ directory.
Open that text file - and you need something else than notepad to open it, because on notepad, the formating goes all awry, and you can't read it properly. (I recommend looking up and installing a nifty little free program called Notepad++)
What you'll see is a name (and path) of a file, followed by columns of data, representing the number of hardware interupts and other events the driver file in question caused during that three minute observation period.
Look through the file, and if there's a problem, you'll see that one of the drivers is producing a LOT more calls than the others.
(For me it turned out to be a Microsoft High Definition Audio driver, that was non-essential anyway. )
When you've identified which driver file is responsible, google the file name to find out what you can about that driver. Is it essential? Could you just remove it? Do you need to disable some service? Or maybe your driver is needed, but you've got a corrupted driver, and you just need to download a new one, or reinstall it from some disc?
For me, I was able to simply rename the offending file (so that it couldn't be found anymore) and disable the associated system driver from my device manager.
I hope that helps - I found it quite a pain to track down this problem, but once I got the RATT program going, it was pretty easy sailing after that. And now my 'puter's working smooth again!
Forgot to explicitly mention it in my earlier post - I'm using windows XP, and can't be sure that everything I did is directly applicable to other windows versions. I think the gist of the way you diagnose excessive hardware interrupts, at least, will be applicable across the board.