Windows XP - Physical memory dumping

This also can come from a faulty ventilation or a faulty RAM (less likely). Manually inspect the temperature of the North and South bridge and check if the fans are running normally. You can also execute a RAM test application.

"You say you've changed the hard drive.

If you have 2 sticks of RAM, then remove one. Try it.
Remove the other. Try it
See if still a problem.

You say you've tried different cables. (I know IDE cables can often be unreliable maybe SATA ones are more reliable..no doubt you use SATA but still try..) As people have said.

Try putting your hard drive in a different port on the motherboard. It may be one port is faulty, then you'll be a bit more sure it's a motherboard issue and have isolated it a bit.

If still a problem then it makes the motherboard a big suspect. But you won't know for sure.

Normally you can't go further than that. But maybe if you find a way to keep the chipset cool or if you check the temp and find a relationship between that and crashing, then you've hit the bullseye. That would be interesting. But that's a bit experimental, and you seem in a rush.. so

Get the motherboard replaced.. you've probably got enough reason to. Then if the replacement will work, you'll know."