Can't run Apple Hardware Test as Mac crashes
Hardware defects

It is likely that some of the hardware that is needed for the hardware test to run, is defect. My personal experience is that this will most likely be one of your 2 RAM DIMMS. You can safely eject 1 and try the test again (and the same goes for the other).

If you run your hardware test from CD/DVD, you can also do this for your HD, and other components.