I would tend to think that there c ould be a problem with one of the memory sticks so I think a runthrough of Memtest86+ would be prudent even though it takes some time.
Please follow these instructions 
exactly.
I would suggest that you download and run the latest version of  Memtest86+ to check your RAM first.
Memtest86+        
http://www.memtest.org/Insert 
one stick  of memory in 
slot 1 and run Memtest on it for at least 
10 complete loops/cycles and if there are no errors then swap it over with the next one and continue untill you have checked all  modules. 
If you have any errors the module is faulty. 
If you have any faulty modules you will have to return the whole kit as they are matched.
Post back when you have done that with the results.