Hi
Well it certainly sounds like a memory problem doesn't it ?
The first thing you need to do is run Memtest on your RAM one stick at a time. 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.
I would also be suspicious of your power supply. The only reason it is still going is because it is a good make. Purchase a good make like Seasonic, CWT, Corsair, Thermaltake, Enermax, Gigabyte, Coolermaster, Antec, etc and try and get one with a single 12V rail if possible. I would advise you to get one of about 650W minimum.