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Windows 7 boot issue - hangs at Classpnp.sys

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This is a copy/paste from another forum I use, so bear with me..


A few days ago I purchased an SSD and did a clean Windows 7 Ultimate x64 installation.

Screenshot of my current system:

C: – Intel 520 120GB
F: – Samsung 1TB, few years old.. not sure on the model anymore.
E: – Western Digital Green 2TB. Few months old.
G: – Seagate Barracuda 1TB ST31000524AS, about a year old.
Now the issue is that this morning, about 3-4 days after the SSD & Windows clean install, my computer wouldn't boot. It just sat on the "Starting Windows" screen, the logo slowly pulsing.

Trying to start in safe mode led to it hanging at trying to load Classpnp.sys.

Straight away I though "Oh no, SSD failure?" and proceeded to unplug all my drives except the SSD — booted perfectly fine. Testing the other drives one by one, I found out that only when the Seagate (G:) was plugged in did the boot hang. Which is an issue beacuse this was where I keep my Uni work, most of my documents, music, and program installations that I don't want to keep on my SSD (like games).

I've got a full backup of this drive now, so it's not exactly scary if it's failing, just annoying to set everything back up.

Here is the really baffling part – sometimes the PC will boot fine. It's usually after i've tried a few boots without the drive plugged in, then plug it in, and it works fine.

Or, another workaround I think is working, is to remove the drive letter before I shut down, and just give it back it's G: letter after booting up again (haven't confirmed this works all the time, could have just been lucky).

I've still got some ideas left for troubleshooting the exact issue, but I just don't have the time to deal with it right now (bunch of assignments due) so i'm just looking for some outside opinions/help to speed up the process.

Now, the Classpnp.sys is supposedly a driver to handle SCSI drives or something, and I have my BIOS running in AHCI – causing an issue with the Seagate?

Is it worth noting that the Seagate is the drive I used prior to the SSD to run the OS from? It's had a clean format since then though.

Am I able to replace the Classpnp.sys file?

Any ideas?



Extra info:

So, a small update. I've got another workaround that's a bit better (doesn't require me to think about anything before I turn the computer off).

If the PC won't boot up, I can restart, enter the BIOS, and switch from AHCI back to IDE. Attempt to boot (this doesn't work anyway, either tries to boot from the wrong disk and gives a grub> prompt, or BSOD if it tries from the correct one), restart when it fails, and set it back to AHCI. Windows will prompt to start normally or run recovery, starting normally works perfectly fine.

Just adds an extra minute or so to booting up, kinda negating half the point of getting this SSD :P

But it's something to think about.

From what I can see, there have been a LOT of people in random places all over the internet that have had an issue with this Classpnp.sys hang, and the cause always seems to be difficult, making it really hard to diagnose :/
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This is a copy/paste from another forum I use, so bear with me..

are you being helped at another forum at this site (G2G)

try setting the bios to default or safe settings..

try repairing the MBR...
also run chkdsk /r on the seagate
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