Evesham Quest A240 Computer freezes after varying period of time?

It is running with XP Professional. The problem has started recently and always freezes with a complete screen of lines of the same pattern repeated when running one of a range of different programs?
Ctl+Alt+Del does not open the active programs box.
It has been suggested that the graphics card may be the cause. do you agree that is is the most likely, if so, what is the most cost effective remedy?