stripey,
I'd say whosyirdaddy is correct in the needing to boot it up with the recovery cd.
It depends on what's happened. Did you install/uninstall anything prior to it failing? Whether you have backups.
Answers based on Windows XP, some of it may work for Vista - not too sure.
If nothing has been changed it could just be a fault with the file system and just needs a "scan disk" run (Seen this 3 times in the last couple of months). Has Recovery Console been setup to run from the Boot menu (the menu that has the Last known good configuration), this is normally not set up by default and would have to have been set up by yourself. If it is, then you can run scan disk from there.
If you've got a windows installation disk you can use that to enter recovery console and run scan disk.
In cases where i've not had the Recovery CD, and recovery console is not set up, i've had limited success with removing the disk and attaching it to another system as a secondary drive and running scan disk from there. You can back up your files as well.. A bit tricky on a laptop though unless you have the appropriate adapter.
You could use a boot disk from another operating system like Linux. This will at least get you to your files and let you back them up. (I did this a couple of weeks ago using ubuntu and backing everything up to an external usb drive. Ubuntu boots as a LiveCD (it doesn't touch your hard disk unless you want it to!))
You may even find that if you use Ubuntu that the act of accessing and reading files on your disk sorts the problem, although i wouldn't claim that this would happen.
I'd try the ubuntu route first to make sure you have a backup.
It depends on what resources you have available. If you have another computer or someone who can download ubuntu for you and burn the iso file properly then give it a try.
If you have more information: model of laptop, which version of windows, what file the blue screen mentions, then there might be another solution.
Long winded i know.... The thing to remember is that you should be able to get to your files and back them up in some way. Hope this helps.