Latitude E6400 with Brand new Windows 7 randomly shuts down while basic office tasks

My employer purchased five Latitude E6400 Laptops, I installed Windows 7 32bit. A few days after I setup the system in question, users stated that the machine shuts down while they were doing work in word, excel, etc.

I have thoroughly tested System RAM (Memtest86 36 Pass 0 Fail), and Hard Disk (seatools extended test, and third party advanced read / write test. Safe to say that the basic hardware is not my issue.

So ... any ideas, questions.

At this point all I can think of is using google and forums to discern an answer.

Any comments or ideas are appreciated.

Thanks