Windows 7 64bit won't boot - 0xc0000225 error - Macbook Pro w/ bootcamp

Hi there, this is also posted in the Apple forums, as I'm running Windows and Mac OSX on separate partitions on a MacBook Pro, but it was suggested I might get more help here as it's a pretty specific Windows problem.
Whilst editing the msconfig setup on my Windows 7 64bit partition (which I've
done a good few times before) I stupidly checked the 'use original boot
configuration' thinking it was a 'return to defaults' synonym.

Now when I attempt to boot into Windows, I get the following error message,
before any Windows logo appears:
'Windows failed to start. A recent hardware or software change might be the
cause. To fix the problem:
1. insert your Windows installation disc and restart your computer.
2. Choose your language settings, and click "Next."
3. Click "Repair your Computer".
Status: 0xc0000225.
Boot selection failed because a required device is inaccessible.'

Corrective steps so far:
I have the original Windows CD from when I bought it, but I can't manage to
make Windows boot from that instead of internal storage, so no startup repair or
restore options which apparently is all I need to fix this error...
I'm, not sure whether this is just because of bootcamp not recognising the
disk properly or my optical drive playing up (which is has done with some disks
pretty much since I bought the mac, although it does boot successfully from the Mac
OSX disk I tried).
I've also tried downloading the same ISO image and creating a bootable USB
flashdrive but that won't boot either - again, not sure whether this is because
bootcamp won't support it (I've heard Apple's firmware doesn't like booting from
flashdrives much), or whether the USB should be formatted differently etc (it's
currently formatted as NTFS but am now wondering if trying again with FAT32
would make any difference).
I've also installed ReFit and am running that successfully, which recognises
the USB disk but also can't boot from it. Tried the MBR and GPT sync tool too
which said there wasn't a sync problem anyway.
I can't access any boot options for Windows (Safe Mode etc), each attempt is
faced with the same error; can only choose to boot Windows or run the memory
diagnostic tool which I doubt would help.
Obviously can't access any BIOS as that doesn't really exist on macs.
Can I replace any specific boot file on the windows partition remotely?

Please help! I'm running out of ideas and really don't want to try and
re-install Windows!

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