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My laptop's CPU is an Intel P8400, rated for operation at 2.26GHz.

However, sometimes it starts running really slow: the computer becomes nigh unusable, and utilities like CPU-Z show clock speeds in the range of 192MHz to 533MHz.

After a while, it will recover. Sometimes it will recover spontaneously, but often I have to reboot it (usually more than once), or shut it down and come back later.

It doesn't seem to be overheating:

  • SpeedFan and the BIOS both shows reasonable temperatures.
  • The problem occurs most frequently when turning on or waking up the computer after it has been off for a while.
  • Leaving the laptop running for a while to "warm up" sometimes fixes the problem (temporarily, of course).
  • The fan does not spin up, and the air coming out of the computer is cool.

I have also eliminated software and drivers as possible causes:

  1. I updated the drivers under Windows 7.
  2. I updated the BIOS to the latest version (even though there was nothing relevant looking in the release notes).
  3. I also tried turning off Intel SpeedStep, but it didn't fix the problem, so I turned it back on.
  4. I gave up on Windows 7 and installed Ubuntu 11.10 instead.
  5. I eventually noticed that my BIOS setup reports the current clock speed, with a ridiculous readout like this:
    • Current clock speed: 192MHz
    • Minimum clock speed: 1.6GHz
    • Maximum clock speed: 2.26GHz

None of these changes had any affect on the problem that I could detect.

I'm guessing that either the motherboard (likely) or the CPU (possible) has failed, but I was wondering if anyone here has ever seen symptoms like this. I've Googled around a bit, but all I'm finding is stuff related to overheating or overclocking.

What could be causing this behaviour? Is there any way I can fix it short of replacing the laptop?

My laptop's specifications:

  • Dell Latitude E6400
  • Intel Core 2 Duo P8400 (2.26GHz, dual core, 45nm, 3MB cache)
  • Intel GM45 motherboard chipset
  • 4GB of DDR2 800MHz RAM
  • 9 cell extended battery (in good health according to the BIOS)
  • About 4 years old (out of warranty)
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Have you tried playing with BIOS cpu settings? I don't know if E6400 has C state but disabling C state on my Dell with i7 helped a lot. – MadBoy Dec 17 '11 at 19:51
@MadBoy Unfortunately, being an OEM laptop, my BIOS is missing a lot of options. I couldn't find a way to control C states. (There's no overclocking type options, either.) There are some third party tools that claim to be able to do that kind of thing from within Windows 7, though, so I could try that later if I reinstall Windows. – Thomas Bockman Dec 17 '11 at 20:40
I have DELL as well and I have that option. Just with newer laptop – MadBoy Dec 17 '11 at 20:50
@MadBoy Yeah I didn't mean to imply that no OEM laptop has such an option, just that, in general, laptop BIOS options tends to be a lot less complete than for DIY desktop boards. My particular system doesn't seem to have any relevant settings other than SpeedStep, which I already tried changing. – Thomas Bockman Dec 17 '11 at 21:16
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Looks like it could be a known issue, or a hardware problem.

Having said that, you might try cleaning the fan out in case it's a heat build up causing it.

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Thanks! That "Throttlegate" link looks very interesting. – Thomas Bockman Dec 18 '11 at 1:26
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