memory test locks up computer

So if I'm running the TechTools Pro memory test, and that consistently locks up the computer, does that mean the RAM is bad or something else is wrong in the system. Normally, I would just expect TechTool to come back and say the memory test failed, but I've seen this one iMac lockup everytime at about 10% progress bar everytime. So I replaced the RAM with new stuff, but it still locks up (arrrgh!!!). Is it possible something else is messed up on the motherboard or chipset?