In this case it was a Vista laptop which the supplier had upgraded in-place to Windows 7 before supplying it (which seems dubious to me) and then the owner had upgraded again to Windows 7 Professional. So it is still just possible that a clean Windows 7 installation is a little more robust than Vista to these extremely aggravating KSODs (blacK Screens Of Death).
I wrote about KSODs in Vista way back, here and here. Essentially there are two flavours, both showing the characteristic black screen with just a white mouse pointer moving around it. The important difference between the two is that one occurs before you log into Windows, the other after. If the black screen occurs after you log on, you have a fighting chance (although it may still be difficult to fix). If the black screen is before you log in then you are in trouble: basically all of Windows' security is aimed at stopping you from changing anything.
In the case of the Vista KSOD-before-login linked above, I never actually managed to fix it - which was deeply frustrating. So this time, when I got a Windows 7 KSOD-before-login I was concerned, but hopeful that I could find a way around it this time.
I did eventually get Windows to boot ... unfortunately not until I had essentially given up, so I ended up trying several things at once and it's not clear which made the difference. And I certainly don't plan to try to recreate the KSOD again just to check them out.
But if you have a KSOD yourself, Vista or Win7, then hopefully some of this may help you do things a little more systematically and find a consistent solution.
IMPORTANT: do not do any of this unless you really know what you are doing in the technical nitty-gritty of a Windows 7 computer and unless you recognise that is you mess anything up it is entirely your own responsibility.
The least damaging of these possible fixes is simply to repair the partition boot sector (I suggest you refrain from fixing the MBR unless you really have to, as many manufacturers put special code in there for recovery partitions and the like). From the W7 repair console this is simply a matter of typing:
Bootrec /FixbootReboot and see if this has helped. This is such a simple thing that it is probably the best first thing to try. Then try the fixes in my earlier post, linked to above, in case one of those helps you. If not, the other thing I did was much more drastic: I opened up file permissions to everyone in the Windows and root folders. This will make a mess of Windows and you will need to do a repair installation to (maybe) fix it - so it is very much a last resort.
ICACLS C:\ /grant "Everyone":FThen, from the root directory:-
ICACLS *.* /grant "Everyone":FAnd finally, from the \Windows directory:-
ICACLS *.* /grant "Everyone":F /t /cIt is unlikely that you need all of these so try them one at a time and see if one of them does the trick.
If you do find a solution to the pre-login KSOD please leave a comment to let me, and others, know how worked for you.