I would advise checking the memory as the first option. It is a fairly time intensive operation but worth doing properly. Use the following instructions and follow them exactly!
Make sure that you use the very latest version of the program.
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.