Out of curiosity, do you still have your original driver disk for the GTX 295? If you do, try out those drivers. They are going to be really out of date, but its worth a shot. The game will give you a message that the drivers are out of date, but you can bypass them by hitting the ESC key when the message comes up.
Let me know.
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Thanks for getting back on this, Dan. Tomorrow I have off work so I will be able to run out and see if I can find a PSU tester (just to make sure there isn't anything wrong with the power supply itself.) Actually, I do have the original driver disks for my cards. So I can try installing those and see if it makes any difference.
I've still installed D2:LOD tho. =)