hey - thanks a lot guys - i appreciate your advice.
i had a look at it, checked the fans which all seemed to be working and gave it a clean. no change - i'm pretty sure the graphics card is fried. to be honest this thing has been a pain ever since i got it and i'm loathed to send it back to the manufacturer for the third time in less than two years. i think rather than get the card replaced i'm going to put the money towards a new machine.

hey aikoworld - thanks for the advice mate. i'll take a look at what you suggested.