BSOD on new Dell Vostro desktop

I've had the same problem they are telling me to run their own DELL diagnostics which I cannot find the DVD for (and its not on boot menu as they claimed), also reseating the RAM. I also pass Memtest and similr, no bother, multiple passes over 12 hours.

They are telling me they cant take it back but I have 1 yr collect and return, what does that mean then? Does that not mean I am allowed to tell them to come and pick it up? It has been like this since day 1.

We had 2 Dell Vostros with the same issue, all we did was swap their RAM over and no blue screens since.

Thanks mate
when you say swap the RAM over, I have 6GB I think in 3 times 2GB sticks. I think the motherboard has 2 blue and 2 black RAM holders, maybe alternating? (Have not opened it up yet as am away until later this week). Are you saying I probably just need to pull them all out and reseat them in a different order, but using the same slots?