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I built a desktop about a year ago that has, until a few weeks ago, been running without a hitch using Windows 7 Ultimate.

Recently, the PC started occasionally rebooting with a blue screen indicating a "PFN_LIST_CORRUPT" error. Also, I've seen at least once the error IRQ_NOT_LESS_OR_EQUAL.

I seem to remember temporarily connecting an internal DVD burner about the same time this happened. I burned a DVD for another machine and promptly removed the drive.

Yesterday, I reformatted the drive and installed Win7 Ultimate x64. During the first install, the PFN_LIST_CORRUPT bluescreen reared its ugly head again. A second install attempt completed with no errors. The fact that this error happened during a clean install leads me to believe that this is not a driver or OS issue.

I also ran the memory diagnostic from the Win7 32-bit install DVD. It completed both passes with no errors.

Periodically, the screen will flicker, as if explorer or the video are resetting. In the event log, I see a series of 8 or so errors indicating that some services unexpectedly stopped, and were apparently reset. These include an HID service and some others (I don't have a list in front of me).

The PC is a Phenom X2 3 Ghz with a 500GB Seagate drive, 4GB of Corsair XMS2 cm2x2048-6400c5c.

Anyone know what would suddenly cause a couple of sticks of RAM to go bad?


I ran memtest86+ for a few hours last night and no problems were detected. However, I noticed at one point that the power supply seemed to go into overdrive, and is making an odd oscillating jet noise that it shouldn't. Time to swap the PS and see what happens.

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It's likely to be hardware... and I'd guess on RAM, though it could be just about any other device.

Testing the RAM is easy enough - get hold of a copy of memtest86+ and run and an overnight test (or at least for a couple of passes through the RAM). Before you do this though, disconnect all internal and optical drive and any extra PCI(e) cards etc.

If the RAM passes, add each device back in one at a time, starting with your boot disk. Because your problem is intermittent, it will be harder to pin down, so you'll have to be patient. If you access to them, see if alternative components make a difference.

Do you do any gaming or other intensive use of the system? If so, are these BSODs connected? It could be a PSU issue if you have a faulty or poor quality PSU, or if you are loading your PSU too much.

The screen flicker can often occur when there is a problem with the gfx card drivers or perhaps with the card itself...

Hope some of this helps...

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I'm not a gamer, but I've got three monitors running with Visual Studio 2010, SQL Management studio, Outlook and some others. – David Lively Apr 29 '10 at 15:55
Then we can probably discount you overloading the PSU - the PSU itself could still be dodgy, however. – CJM Apr 30 '10 at 10:13
PSU turned out to be fine; the RAM was the culprit. Crucial replaced it with a minimum of fuss. – David Lively Aug 19 '10 at 18:49
Just goes to show why decent branded RAM is desirable. Any RAM can fail, but the better brands have better RMA services in place. – CJM Aug 20 '10 at 12:27

IRQ_NOT_LESS_OR_EQUAL is one of those gems that can be caused by an infinite number of things. Though in your case it is almost certainly hardware fault/damage if it persists through a reinstall and cropped up when installing a drive.

Did you use proper anti-static measures/ground yourself when working with the PC?

Was the PC turned off when you conneccted the drive? (I don't mean to insult, but I've spoken to people who have tried to put RAM in while a machine was switched on)

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I'm not insulted - I fried enough equipment in my younger days. Yes, everything was unplugged and I was nicely de-staticified. – David Lively Apr 29 '10 at 15:52

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