Hi Medway
The 'BSOD' or Blue Screen of Death is one of those things which happens to a corrupted part of the Windows operating systems files/folders. It can't be diagnosed here over the web as there could be a thousand different reasons or files or drivers or updates that 'may' have caused this.
To start - has the user recently installed any software? any drivers perhaps for a new printer or scanner or webcam etc? has the PC been well maintained and the BSOD appeared 'suddenly'? or was the PC getting worse and worse over time in terms of speed, responsiveness and now has the BSOD ?
It 'may' be as simple as running in safe mode, and updating a printer driver to the latest version, or it could be as catastrophic as a beyond repairable corrupted Windows directory.
If it's the latter - there will be expense involved at fixing the issue - and the good news is it IS definitley fixable (worst case is that it'll need a complete re-install of windows)
Hope this helps a bit - Cheers, DtM! West London & Slough UK!