You should be able to press a button before it starts on the first screen on boot up and this should stop it,you only have 10 seconds i think though.But if you are having shut down errors it may be worthwhile finding out whats causing the errors.
Thanks to all who replied to my previous post 'How to stop file system checking in Windows XP' - click here
Sorry, I did not make it clear that the blue screen appears almost immediately after switch on and before the desktop appears. I think, therefore, that the solution posted by Acolyte is the one most likely to work - the only problem is the short time limit and I don't know which key to press!
The next problem is that when all the disks have been checked I get the message 'The second NTFS boot sector is unwriteable' before it then goes on to load the desktop normally!
As this disk check is now appearing every time I switch on, it looks as if there is something wrong with the hard disk. Is there any way to find out what is causing the error and to correct it.