You could also try burn in tests to see.
Memtest has a bootable CD so you can just boot and test all the memory:
http://www.memtest.org/
HWMonitor can tell you what all the temperatures and stuff say:
http://www.cpuid.com/hwmonitor.php
(though interpreting the results properly can be tough, it's easy to get results that look horrible but actually aren't)
With MWMonitor you can use Prime95 to stress the computer and watch MWMonitor to see if anything overheats:
http://www.mersenneforum.org/showthread.php?t=12155
It could still be heat, if a heatsink on the memory isn't right, or if they're installing the CPU heatsink just a little wrong, etc.