Boot failure following Windows 8.1 update. shows reason: irql_not_less_or_equal

Question

Hi,
I have the dreaded BSOD with irql_not_less_or_equal boot failure. 
The PC was running Vista when bought, which was subsequently upgraded to Windows 8. This was done via an online purchase & download of the Windows 8 Upgrade, so I do not have any installation media. I have also updated (again online, so no physical media)
to Windows 8.1
I have recently had to shut the PC down (it usually stays on all the time), but now it refuses to boot, going straight to the new style BSOD, showing 'irql_not_less_or_equal', which then restarts in to the system restore menu.
I have tried to remove some peripherals - removing the video card (now using the display adapter on the MoBo), a USB 3 card & a USB head-set dongle - which  has improved the situation a little - it now boots to the log-in page (sometimes), but will
BSOD after about 10 seconds, regardless of whether I am fast enough to log-in, or not.
I have tried (from the System Restore menu) to do a restore to a previous state, but it doesn't seem to be able to find the restore points.
Note, the BSOD occurs if I boot into 'Safe' Mode, or do a normal boot. 
The bottom line is:...
I can't boot to Safe Mode, get to any system maintenance tools, so I can't disable/uninstall any drivers.
Windows 8 & the 8.1 update were purchased online & downloaded, so no boot disk(s).
The recovery points I have made do not seem to be accessible.
Any advise on how to proceed?
cheers
Paul

Answer 1

now boots to the log-in page (sometimes), but will BSOD after about 10 seconds, regardless of whether I am fast enough to log-in, or not.
That should be enough time to get to the Shift-Restart option.   <eg>
Since you can see what you're doing you don't even have to do the backwards method that I was long proposing so that users who were trying to do this in the dark would be able to bypass their password field.   But maybe using a set of Backtab (Shift-Tab)
Shift-Space would be more efficient anyway?
Here is an example of an explanation of the technique:
http://social.technet.microsoft.com/Forums/en-US/37eff8a6-74a3-4775-90d7-e0aa86c68424/windows-8-black-screen-at-boot?forum=w8itprogeneral#0dc40edd-4e3b-466b-b4af-37c532eb844a
<quote>
In order to try to avoid hitting the Password field in this uncertain state I suggested using Backtab (e.g. Shift-Tab) to do the navigation. Fortunately, the pressing of Shift- would solve the problem of whether you were on the Lock screen or already on
the Login screen. So the iteration would be Shift-Tab, Shift-Space (Fortunately, the Restart item is at the bottom of the Shutdown menu.)
</quote>
HTH
Robert Aldwinckle