Post deleted by Sadoldman

In reply to a post by ian72:

If you are confident it is worth trying the graphics card then I could recommend talking to Novatech. They have some very knowledgeable guys and should be able to point you to a card that would fit your machine. Be aware though that this is a likely cause rather than a definite cause so it may be that a new card doesn't fix the issue.

SOLVED!! In instances where the sound continued after the screen went blank made me confident it was not a PC shutdown. After a successful test with a borrowed card from another PC I decided to take the plunge and bought a new graphics card. Tests since fitting this card have proved positive with no more issues of a blank screen.

Thanks for all your suggestions.