I thought I would record the following experience in case it helps others who encounter the same problem. I have an old Dell Latitude D830 laptop and generally leave it in standby mode at the end of the day.
Standby mode uses little power and makes the slow Windows XP reboot unnecessary. However, last week I was away from the office and the machine in standby mode, and detached from the power supply, apparently ran out of battery power. When I came to power up the machine, rather than springing back from standby mode, it began a normal reboot sequence. However, this reboot sequence was far from normal in its ending. After the Windows XP logo appeared with its blue progress bar, the screen suddenly went completely black.
Very strange and unsatisfactory behavior! Googling through the various sites discussing this topic, I quickly came to appreciate that there are a multitude of ways in which this tedious effect can be achieved. Rebooting in safe mode or VGA mode worked fine, but any attempt to get to the normal screen resolution resulted in the blank screen after the Windows XP logo part of the reboot sequence.
To solve the problem I tried rebooting in safe mode and reloading graphics drivers as originally downloaded from Dell. This did not solve the problem. I then tried just using the machine with remote desktop, after booting it into VGA mode. This worked well, but wasn't quite what I was used to, and certainly did not constitute a fix, and so I Googled further. I tried 'repairing' the operating system using a Windows XP disk. (That was a mistake - see below). Eventually, I ran into a site which described how someone logged onto the machine, although the screen was black. So - having nothing to lose, I tried that. I typed username - and tab - and password a few times. Something in the blankness was happening as their were some typical Windows XP clonking sounds emitted from the machine. Then I must have hit the correct sequence, as the display suddenly lit up, and carried on working as though nothing had ever happened.
Of course, the Windows XP repair attempt had the effect of removing all the vital operating system updates that had been put on the machine. So, a large Windows update was then required to restore SP3 and all the other updates thought to be vital to my security. So, the conclusions are firstly that Windows XP and standby mode can be fragile under some rare circumstances. Secondly, curing tedious Windows XP start up problems can be mysterious. I speculate that my habit of putting the machine into standby mode may be quite risky when perilously short of diskspace. Probably at some point the standby mode program decides that the battery will expire soon and decides to write everything out to disk, but without checking properly that there is enough diskspace to save everything. Then, somehow or other, some special state for the graphics card of blankness (because the lid is closed) is saved, and the machine crashes. This state will be overwritten the next time someone logs on successfully. However, the next logon is effectively prohibited by the fact that the screen is blank.
Hence, users are forced into the rather tedious process of either wiping the machine and starting again. Or buying another machine and making another donation to Microsoft in the process for another, equally buggy, operating system.
But - if you have a blank screening Windows XP laptop, that almost boots but not quite, try typing in your credentials at what should be the log in screen. You may find that this clears the problem - and although it is not as satisfying as repairing the operating system, replacing graphics drivers, or buying a new machine, it may just get your machine going again.