stop error screen/ physical memory dump

i have have my dimension 2400 for less than four months. over the past months i have encountered on more than one occasion the following error screen:

A problem has been detected and windows has been shut down to prevent damage to your computer.    If this is the first time you've seen this stop error screen, restart yur computer. If this screen appears again, follow these steps  -  check to make sure you have adaquate disk space, if a driver is identified, disable driver/check for driver updates/try changing video adapters...       ...physical memory dump complete.   (there is never a driver identified)

and on one occasion, when trying to shut down, i came to a screen letting me know that my "system crashed because the RAM containing Windows was corrupted," and that "the nature of the crash suggests a hardware corruption" 

i have had help from experienced people on the forum with hijackthis, spybot, and adaware..    

-jim